SECTION III.

In the following section of our report we shall have frequent occasion to refer to a series of investigations conducted by the author in the City of Boston during the 1920 influenza epidemic. We will explain in some detail at this point the nature of the work done and the methods used, in order that the subsequent references will be readily intelligible.

AN INVESTIGATION OF INFLUENZA IN BOSTON DURING THE WINTER OF 1920.

Following every widespread epidemic interest centers in the question as to how much havoc the disease has wrought, what proportion of the population fell victim, and how many of these died. With regard to influenza the vital statistics of all countries are decidedly insufficient in furnishing this information.

In nearly all countries influenza is not a reportable disease. Usually, as was the case in the United States in 1918, the disease was made reportable during the epidemic, but this took effect usually at least two weeks after the epidemic had started in a community. Further, there is probably not a single community in which the reported cases of influenza reach to anywhere near the total of actual cases. The question of diagnosis, which is not always easy even in the presence of a pandemic, causes some physicians to hesitate to report cases. Other physicians “play safe” and report nearly everything as influenza. Finally, in the period of an epidemic, the physicians are so pressed with caring for the sick that they very naturally neglect to report cases as they occur.

It becomes necessary, therefore, in collecting evidence in civil populations, of the morbidity and fatality from influenza, to obtain additional information to that available to the Health Officer.

The method which may be relied upon to give the most accurate data consists in house-to-house surveys made soon after an epidemic, in which competent inspectors obtain detailed information concerning the illness or freedom from illness of every individual in the areas canvassed. The majority of individuals interviewed will not have had the disease, and it is therefore essential that in such a census a large enough population be covered that the resulting figures will be truly representative of the population at large.

Toward the end of January, 1920, when the recurrent epidemic was at its height in Boston, the author undertook with the aid of thirteen trained social service workers, and one physician, who was a graduate of the Harvard School of Public Health, to make a sickness census of 10,000 individuals. Six districts were chosen in different sections of the city, representing six different economic and social groups. Great care was exercised in selecting the districts, so that the population in each might be as homogeneous as possible regarding economic and sanitary status, as well as race, and living conditions in general.

We have sought to clarify and to abbreviate our description of the characteristics of the various districts by incorporating a map, together with photographs of typical streets in each district. One who compares these streets as they are seen in the photographs would scarcely find it necessary to enter the buildings in order to discover the living conditions of the occupants (Chart XIII).

CHART XIII.

Map of greater Boston showing the distribution of the districts covered by the author’s house census. ]

District I includes an Italian population of 2,000 individuals, one-half of which live in the most congested portion of the city (see photograph) known as the North End, while the other half, living in East Boston, are slightly less crowded.

District II, in South Boston, consists of 2,000 individuals almost entirely of Irish race stock.

FIG. 1.—District 1. Italian tenements. Very congested and very poor. ]

District III, like District I, consists of three groups living in very similar environment to the two groups of the first district, but composed chiefly of Jewish race stock of various nationalities. The photograph for this district represents the area in the “West Side” near the Charles River Basin. The area in the “South End” is of similar type, while the area in East Boston is housed similarly to the Italian district in East Boston. The dwellings in both of these latter districts correspond to those shown in the second photograph of District II.

While the first three districts comprise tenement areas, some poor and the remainder very poor, Districts IV and V represent the middle class, and consist nearly entirely of “Duplex” and “Three-Decker” buildings. The first of these comprises 1,000 individuals of mixed race and nationality, the type broadly spoken of as American. The second consists of a Jewish population of 1,600.

FIG. 2.—District 2. Irish tenements. Congested and poor. ]

FIG. 3.—Another street in the Irish tenement district. ]

FIG. 4.—District 3. Jewish tenements. Very congested. Very poor. ]

FIG. 5.—District 4. Middle class. Mixed American population. ]

FIG. 6.—District 5. Middle class. Jewish population. Moderately well-to-do. ]

FIG. 7.—District 6. Well-to-do population. Mixed American. ]

In District VI are included 1,400 individuals belonging to the well-to-do and moderately wealthy families of Brookline.

The six districts may be considered as representative of the various strata of society, so that we are enabled to study the influenza and its mode of action under varying environment. We have selected areas in the city consisting of households or homes rather than boarding houses and rooming populations. After a few attempts in the latter group we became convinced that the information obtained in rooming houses was utterly valueless. In the Jewish districts we were able, through the kind co-operation of the Federated Jewish Charities, to use trained Jewish Social Service Workers, each of whom had previously worked in the district assigned to her, thereby possessing the confidence of the inhabitants. They were also able to speak the language. One-half of the Italian district was surveyed by an Italian physician and the other half by an American Social Service Worker who knew the Italian language.

The information obtained was recorded on printed forms, which were filled out in accordance with detailed written instructions. Form “A” contained the necessary information concerning the family as a whole, including statistical data of each individual, description of the dwelling, of the sanitary condition, of the economic status, etc. Form “B” was filled out for each individual and gave detailed information as to the occupation and illnesses during the 1918–19 or the 1920 influenza epidemics, or during the interval. Form “B” was so arranged that the inspector was not called upon to make the diagnosis of influenza, but to record the various symptoms as described by the patient. The decision as to the diagnosis was made later, by the author. All blank spaces were filled in with either a positive or negative answer, so that the reviewer knew that all questions had been asked and answered. (See Appendix.)

The inspection was begun on February 9th, at the height of the epidemic. All records were turned in and reviewed by the author, who blue-penciled obvious inaccuracies and incorporated directions and questions in those instances where he desired further information. The records were then returned to the inspectors who, at the termination of the epidemic early in March, surveyed the entire 10,000 a second time, checking up their first record, correcting any inaccuracies, and adding records of additional cases of influenza which had occurred in the interval.

The most careful statistical surveys and compilations are not without error. We have gone into considerable detail in the preceding description in order to demonstrate the several checks that have been made upon the work, without which information others would be unable to judge of the accuracy or value of our work.

Diagnostic standards for the 1918 epidemic.—All cases of illness recorded on the reports, which have occurred during either the 1918 or the 1920 epidemics, or in the interval between them, have been put into four groups as regards diagnosis of influenza. Cases are designated as “Yes,” “Probable,” “Doubtful,” and “No.”

Cases of illness occurring during the months of 1918 and 1919 in which influenza was epidemic and in which the patient remembers that he had the more definite symptoms, (fever, headache, backache, pain in the extremities, pneumonia) and in which he was sick at least three days and in bed at least one day, have been designated as “Yes.” The symptoms chosen are those most likely to be remembered. The individual frequently does not remember all. Statements of the absence of fever are often unreliable. Usually the headache, backache or pain in the extremities, or even all of these are well recollected.

Cases occurring particularly during the epidemic period in which the more definite symptoms are unknown, but who were sick three days or longer and who were in bed at least one day, were probably influenza. This is particularly true if there were no other symptoms suggestive of some other definite disease. Such cases were designated “Probable.”

Cases have been designated as doubtful when the evidence of illness falls short of the above desiderata. Cases of true influenza may fall into this group, either because of the extreme mildness of the symptoms and course or because of the inaccurate memory of the individual concerning the events of his illness sixteen months previously. Our results show that the group of doubtful cases is relatively very small and the number of true cases lost in this group will be negligible.

One important reason for adhering to the above classification is that it corresponds closely with that used by Frost and Sydenstricker, so that our results may easily be compared with theirs.

Standards for 1920.—For 1920 the illnesses were so recent in the minds of the patients that we have required rather full information for making the diagnosis of “Yes.” For this designation certain symptoms are arbitrarily required. Certain additional symptoms, if present, serve to strengthen the diagnosis of influenza. The required symptoms are fever, confinement to bed for one day or more and at least two out of the following three, headache, backache and pain in the extremities. The additional symptoms which influence the classification are sudden onset, prostration, lachrymation, epistaxis, and cough.

Cases designated as probable are those in which the symptoms as enumerated above are incomplete in one or more details, but yet in which the diagnosis of influenza would be justified. “Probable,” therefore, means that the case is to be accepted among the list of true influenza cases. This is particularly so when the case occurs during the epidemic period.

“Doubtful” applies to those cases in which the evidence although suggestive of influenza, is not complete enough to warrant such a diagnosis. The doubtful feature may be in the lack of too great a number of the symptoms enumerated, or the presence of symptoms which might be due to some other disease. Certain cases occurring at the same time with other cases of typical influenza in the same household, and which would otherwise have been recorded as doubtful, have been marked either “Probable” or “Yes.”

Standards of severity.—A purely arbitrary classification of severity has been adopted. Probably no two observers would agree exactly on a classification of this nature, but for the purposes of this study the following will suit all requirements provided the standard used is carried in mind throughout the comparison.

If a patient with influenza is under medical care, and the case is one of ordinary severity, the usual period in which the individual is advised to remain in bed is one week. This is the basis of the criteria of severity.

Mild.—A case is recorded as mild if the individual has remained in bed three days or less; Average, if in bed four to seven days; Severe, if in bed over seven days. Pneumonia. This designation is added to that of “severe” only in case the physician made such a diagnosis, or if the evidence under “symptomatology” leaves no doubt as to the condition.

Examples of individual exceptions to the preceding general classification are as follows: An individual in bed two days, but sick for three weeks might be recorded as average. A mother, with a family of sick children and who spent no time in bed may have been a severe case of influenza. In fact, we have allowed ourselves a certain latitude in individual cases in classifying both the diagnosis and the severity of the disease.

In the final tabulation we have included both the “Yes” and the “Probable” as being cases of influenza. This has been done after a careful comparison of both groups.

As a check upon the reliability of the work we have compared our results for the 1918 epidemic with those reported by Frost and Sydenstricker and have discovered that with regard to the general subject discussed in both studies there is close agreement. This is important in view of the long period that has elapsed between the first pandemic and the time of our survey, and because we are unable to compare our tables of incidence for 1918 with those for the city or the state at large. Our own records do not place the date of occurrence of the disease in 1918 any more closely than by month.

We have compared our 1920 incidence curves with those of Massachusetts and find a close correspondence, particularly in the date of onset, peak, and disappearance of the epidemic. We have done likewise for the occurrence of the disease in the city of Boston at large (Chart XIV).

In the past but few house-to-house canvasses have been made with relation to influenza. Auerbach, following the 1889 epidemic, collected statistics on 200 families distributed throughout the city of Cologne. Abbott, while not conducting a canvass, did obtain a certain amount of valuable information by letters addressed to physicians, institutions and corporations throughout the State of Massachusetts.

There is fairly abundant literature on the disease as it occurred in institutions. Moody and Capps, in a study of the epidemic in Chicago in December, 1915 and January, 1916, made a survey of the personnel and inmates of four institutions in that city. Among other rather numerous statistical compilations from institutions we may mention that of Hamilton and Leonard which was devoted particularly to a study of immunity, and that of Stanley at San Quentin Prison, California.

Garvie has reported his personal experience with influenza in an industrial area and discusses the disease as it has occurred in families in his private practice.

Carnwath reports a “block census” undertaken by Dr. Niven in Manchester, England. This is of the same nature as our own work. Reeks has made a detailed house survey of 2,757 persons in New Britain, Connecticut. D. W. Baker has conducted somewhat similar surveys for the New York Department of Health, and Winslow and Rogers quote the excellent record of the Visiting Nurse Association of New Haven, in which they have information for all of the families cared for by the nurses. This, however, is a collected group and does not correspond with the so-called block census.

CHART XIV.

Chart showing the actual incidence of influenza in Boston by weeks and the actual incidence among the 10,000 individuals surveyed by weeks during the first three months of 1920.

Full Line—incidence in the entire city based upon reports to the Health Commissioner.

Dotted Line—incidence in the six districts surveyed. ]

The most comprehensive and detailed work that has been done in this line is that reported by Frost and Sydenstricker and by Frost, the first being the result of a canvass of 46,535 persons in Maryland, and the second a similar report based on a canvass of 130,033 persons in several different cities of the United States. We shall have occasion to refer to these later.

MORBIDITY.

There has been great actual variation in the morbidity from influenza in the various epidemics and even in different localities during single epidemics. Previous to 1889 there were no reliable statistics for the disease incidence, and subsequent to that date the records, for the reasons previously mentioned, have still been not entirely adequate.

In the history of influenza morbidity, as in that of its mortality, we must content ourselves for information prior to the nineteenth century with the very general estimates made by contemporary historians. During the last century the statistics have been more numerous and more nearly correct. As far back as the first recognized pandemic, 1510, the extremely high morbidity has been a recognized characteristic. Thomas Short in speaking of this pandemic says, “The disease ... attacked at once and raged all over Europe, not missing a family and scarce a person.”

Pasquier in 1557 spoke of the disease as common to all individuals, and Valleriola describes the widespread distribution of the epidemic throughout the whole of France during that year. It spared neither sex, age, nor rank, neither children nor aged, rich nor poor. The mortality, however, was low, “children only, dying.” Again, Thomas Short remarks, “This disease seized most countries very suddenly when it entered, catching thousands the same moment.”

Of the second pandemic, 1580, Short says, “Though all had it, few died in these countries except such as were let blood of, or had unsound viscera.”

Thomas Sydenham remarks that in the epidemic of 1675 no one escaped, whatever might be his age or temperament, and the disease ran throughout whole families at once.

Molineux recorded concerning 1693, “All conditions of persons were attacked, those residing in the country as well as those in the city; those who lived in the fresh air and those who kept to their rooms; those who were very strong and hardy were taken in the same manner as the weak and spoiled; men, women and children, persons of all ranks and stations in life, the youngest as well as the oldest.”

Schrock tells us that in Augsburg in 1712 not a house was spared by the disease. According to Waldschmidt in Kiel, ten and more persons were frequently taken ill in one house, and Slevogt says that the disease was fearful because so many persons contracted it at the same time. The disease was, however, not dangerous, for Slevogt continues: “Fear soon vanished when it was seen that although it had spread all over the city, it left the sick with equal rapidity.”

It is estimated that in the epidemic of 1729–1730, 60,000 people developed the disease in Rome, 50,000 in Mayence, and 14,000 in Turin. In London “barely one per cent. escaped.” In Lausanne one-half of the population, then estimated at 4,000, was stricken. In Vienna over 60,000 persons were affected. In the monasteries of Paris so many of the inmates were suffering from the disease that no services could be held.

Huxham is quoted in Thomson’s “Annals” as declaring concerning the epidemic of 1732–33: “Not a house was free from it, the beggar’s hut and the nobleman’s palace were alike subject to its attack, scarce a person escaping either in town or country; old and young, strong and infirm, shared the same fate.”

Finkler writes as follows concerning the epidemic of 1758: “On Oct. 24th, Whytt continues, the pestilence began to abate. He is not sure whether this was due to a change in the weather, or because the disease had already attacked most people, although the latter seems more plausible to him, particularly as he says that ‘in Edinburgh and its vicinity not one out of six or seven escaped,’ and in other localities it is said to have been even worse. In the north of Scotland also, the epidemic was greatly disseminated from the middle of October to the end of November. A young physician wrote to Robert Whytt: ‘It was the most universal epidemic I ever saw, and I am persuaded that more people were seized with it than escaped.’ This same physician reported that ‘it was not at all mortal here.’”

In the epidemic of 1762, we learn from Razoux, de Brest, Saillant, Ehrmann, that the morbidity was great while the mortality was low.

According to Grimm, nine-tenths of the inhabitants of Eisenach contracted the disease in 1767.

Daniel Rainy, of Dublin, in describing the invasion of an institution in 1775–76, tells us that from among 367 persons varying in age from 12 to 90 years, 200 were taken sick. Thomas Glass says: “There sickened in Exeter Hospital all the inmates, one hundred and seventy-three in number; one hundred and sixty-two had coughs. Two or three days after the hospital was invaded the city workhouse was attacked; of the two hundred paupers housed there only very few escaped the disease.”

Gilibert described an extraordinary morbidity in Russia in 1780–81.

Metzger says that in 1782 the Russian catarrh was so universal during the month of March that in many houses all the inhabitants were attacked. During this period, “in St. Petersburg, 30,000, and in Königsberg, 1,000 persons fell ill each day;” in Rome two-thirds of the inhabitants were attacked; in Munich, three-fourths; and in Vienna the severity of the epidemic compelled the authorities to close the theaters for eight days.

The epidemics of 1788–89, 1799–1800 and of 1802–1803 were characterized by a relatively lower morbidity than that of 1830–32, in which the morbidity was again enormous. Likewise in 1833, the morbidity was very great. In Prague “scarcely a house was spared by the plague.” In Petrograd, 10,000 persons were attacked; in Berlin at least 50,000. These are the figures of Hufeland. The Gazette Médicale records the morbidity as being four-fifths of the total number of inhabitants of Paris.

In 1836, according to Gluge, 40,000 persons suffered from the disease in Berlin alone.

In London, in the 1847 epidemic, it has been calculated that at least 250,000 individuals took sick, and in Paris, according to Marc d’Espine, between one-fourth and one-half of the population developed the disease, and in Geneva not less than one-third.

Leichtenstern informs us that in 1890 the early reports were made by clinical men and were mere presumptions. They were almost universally higher than the later statistical findings. The early estimates for the morbidity in several German cities were from 40–50 per cent. On the other hand, one of the highest statistical reports recorded by Leichtenstern was for Strasbourg in which 36.5 per cent. of the individuals became sick. The average morbidity reported by him ran between 20 and 30 per cent. The difference is accounted for in part by the fact that some of the very mild cases were not recorded in the statistics, and in part by the tendency in giving estimates, to exaggerate.

Auerbach has collected the statistics of 200 families distributed throughout the city of Cologne. He found that 149 of these families (75 per cent.) were attacked. In these, 235 were ill—59 men, 95 women, and 81 children. The larger number of women was explained as due to the illness of the female servants. He estimates each family as consisting on an average of six individuals, and concludes that 20 per cent. were taken with the disease.

Following the 1889 epidemic, Abbott concluded, on a basis of questionaires sent out to various individuals and institutions in the State of Massachusetts, that 39 per cent. of the entire population had been attacked, in all about 850,000 persons.

Moody and Capps, in December, 1915, and January, 1916, made a survey of the personnel and inmates of four institutions in Chicago, the Michael Reese Hospital, the Illinois Training School for Nurses, the Old Men’s Home, and St. Luke’s Hospital Nurses Training School, making a total of 677 persons surveyed, of whom 144 developed influenza, making a percentage morbidity of 21. They remarked that there were many others with colds who remained on duty and were not included in the table and were not diagnosed as influenza.

We have already described the relatively low morbidity and mortality in the early spring epidemic in the United States. According to Soper, the total number affected in March, 1918, at Camp Forrest and the Reserve Officers Training Camp in the Oglethorpe Camps was estimated at 2,900. The total strength at that time was 28,586. The percentage morbidity then was probably a little over 10 per cent. Dunlop, in describing the May, 1918, epidemic in Glasgow, says that it was more limited in extent, as well as milder, than the later epidemic.

It has been estimated that in the autumn epidemic in the United States Army Camps one out of every four men had influenza, and one out of every twenty-four men encamped in this country had pneumonia. During the four autumn months of 1918, 338,343 cases of influenza were reported to the Surgeon General’s Office; there were 61,691 cases of pneumonia.

Woolley reports that among the soldiers at Camp Devens, Mass. 30 per cent. of the population was affected.

At Camp Humphreys, 16 per cent. of the entire personnel developed the disease. The camp had an average strength of 26,600 individuals. Fifty-two per cent. of the entire number of cases occurred during the peak week, which ended October 4th. The outbreak began September 13th and ended October 18th.

Hirsch and McKinney report that an epidemic of unusual virulence swept with great rapidity through several organizations in Camp Grant between September 21, 1918, and October 18, 1918. During this time 9,037 patients were admitted to the Base Hospital, representing about one-fourth of the strength of the camp, and of these, 26 per cent. developed pneumonia. About 11 per cent. of the total admissions or 43 per cent. of the total cases of pneumonia died.

Referring to the report of Howard and Love, we quote as follows: “It is probable that practically all susceptible human material in infected camps suffered from an attack of the disease during the continuance of the epidemic. The records from various camps indicate that from 15 to 40 per cent. of commands suffered from an attack of the disease. These records, as previously stated, do not indicate in full the true incidence of the disease. Certain good results were accomplished in some camps by the application of effective and early isolation of patients and suspects and other measures generally recognized as of value. It was sometimes possible to retard the progress of the epidemic and cause it to be spread over a longer period of time. The epidemic thus became less explosive in character, and fewer people were under treatment at the same time. It was possible to take better care of the sick and thus reduce the incidence of and deaths from complicating pneumonia. It has not been shown that such measures accomplished reduction in the absolute number of cases of influenza occurring in one command as compared with another.

“The ‘cantonment’ group of camps gave a much higher death rate from influenza and its complications than the ‘tent’ camp or ‘departmental’ group. At first glance it would appear that the different housing conditions and the more marked overcrowding in cantonments at the time would fully account for this divergence. Closer study, however, leads to the conclusion that geographical location was a factor of equal or greater importance. It is well known that the disease was most virulent and fatal in the northern, eastern and middle west states, a district in which cantonments predominated. In the southern and Pacific coast states, where the most of the tent camps were located, a milder type of the disease prevailed, with fewer resultant fatalities. Camp Lewis, Washington, and Camp Gordon, Georgia (both cantonments), had relatively low death rates, approximating those in nearby tent camps. On the other hand, Camp Syracuse, New York, and Camp Colt, Pennsylvania (both tent camps), suffered severely and reported death rates approximating those of cantonments in the same geographical district.”

Three waves of influenza are reported by Stanley at San Quentin Prison. During the early wave it was estimated that over 500 of the 1,900 men in the prison population were ill. The wave lasted for a little over two weeks. In the second epidemic there were 69 cases in all, ten per cent. of which developed pneumonia, with two deaths. There were fewer ambulatory cases than in the first. Three and seven-tenths per cent. of the population was attacked in the second epidemic, as compared with 27 per cent. in the first. In the third epidemic there were 59 cases, with no pneumonia and no deaths.

Hernando estimates that in the Philippine Islands, 40 per cent. of the total population of 7,000,000 was stricken with the disease. The epidemic began in June, although it did not become severe until October. The group of ages that suffered most were those between ten and twenty-nine years. Hernando does not believe that the disease was imported because cases were reported before ships arrived from infected countries. After the importation of cases from elsewhere the disease assumed the more severe form.

Armstrong, in reporting a survey of 700 influenza convalescents in Framingham, Mass., remarked that 16 per cent. of the entire population were infected with influenza. Reeks, in a house survey in New Britain, Connecticut, found from among 2,757 persons that the morbidity rate reached 234 per thousand. Dr. Niven found in his block census in Manchester, England, that of 4,721 individuals, 1,108 (25 per cent.) had developed the disease. Fourteen and eight-tenths per cent. of the population were attacked in the summer and 10.4 per cent. during the autumn and winter.

Frost found in his survey of 130,033 individuals that the percentage of the population attacked varied from 15 per cent. in Louisville, Ky., to 53.3 per cent. in San Antonio, Texas, the aggregate for the whole group being about 28 per cent. He remarks that this agrees with scattered observations in the first phase of the 1889–1890 epidemic, when the attack rate seems to have varied within these limits. In five of the localities studied, geographically widely separated, the incidence rate varied only within a narrow limit, from 200 to 250 per thousand. Variations in attack rate showed no apparent consistent relation to geographic location or size of community, or to the rapidity of development of the epidemic.

In a house-to-house survey of 10,000 individuals in Boston the author found that in the winter of 1918–19, 19.71 per cent., or one-fifth of the entire population had developed the disease. It should be pointed out that while the standards used in this survey are entirely comparable to those used by Frost, the author has, contrary to Frost’s method, not included in his group of positive cases those classified as “doubtful.” This would raise the total incidence to a certain extent, but we feel convinced that by omitting the doubtful cases we have approached nearer to a correct picture of the epidemic as it actually occurred. As will be seen from Chart XVI there was no great variation in the different districts studied, with the exception of Districts IV and V. Districts I, II and III were in the tenement section of the city, while District VI was in one of the finest residential parts of Brookline. Districts IV and V were midway between these two extremes as regards economic and sanitary status, as well as extent of crowding. The lowest incidence was in the Irish tenement district. The highest in a middle class Jewish population.

CHART XV.

CHART XVI.

In the 1920 recurrence we found that 9.55 per cent., or one-tenth of the entire population, suffered from the disease, and the arrangement of districts in order of incidence was very little changed. The Irish community suffered least; the two middle class communities most. The well-to-do district in Brookline had the next lowest incidence in 1920. That the high recorded incidence in middle class districts was not due to more accurate or more thorough work on the part of the inspectors is indicated by the fact that a great part of the work on Districts IV and V was done by the same individuals who inspected Districts II and III.

One-fifth of the population studied developed the influenza in 1918–19, and one-tenth of the same population suffered in 1920.

We may agree with Winslow and Rogers, who conclude that the proportion of the population actually affected by the influenza epidemic in 1918 varied between 200 and 400 per thousand.

Relation of sex to morbidity.—Abbott concluded from his studies in 1890, that the weight of testimony appears to favor the statement that persons of the male sex were attacked in greater number and with greater severity than females. Leichtenstern reached similar conclusions. In the epidemic of 1889, the males were attacked more frequently than the females. He attributes this to two causes: first, the greater exposure to infection, and; second, the fact that strong, robust individuals are more frequently attacked.

It is amusing to compare this explanation with another found in the Medical Supplement to the Review of the Foreign Press for March, 1919. “A Spanish mission composed of Maranon, Pittaluga and Falco visited Paris last October to collect information as to the identity of the Spanish epidemic with the world pandemic of influenza. They found that the epidemics in France and Spain were absolutely identical from the epidemiologic, bacteriologic and clinical standpoint. The great majority of the severe cases in both countries occurred between the ages of 16 and 40. Both in France and Spain more females than males were attacked, which was possibly explained by the greater tendency of the former to lead an indoor existence.”

Jordan, Reed and Fink, working in Chicago, found very different results. They could discover no noteworthy difference among the pupils in high school and elementary school. The attack rate was 230 for the boys and 231 for girls. One sex was presumably as much exposed as the other.

Among the employees of the Chicago Telephone Company, on the other hand, the men were affected in considerably lighter proportion than the women (151 per 1,000 as compared with 233 per 1,000 for women). Jordan believes that the age factor was largely responsible for the difference as the women employees are as a rule of much lower average age than the men.

Frost found that with few exceptions the attack rate at all ages was somewhat higher in females than in males. The total excess of incidence in females was six per cent., which ranged from an excess of nineteen per cent. in the highest locality to a deficiency of two per cent. in the lowest. Only two of the eleven localities surveyed showed a lower incidence among females than among males.

When the sexes were compared in different age groups, the female was found to be higher than the male in each age period except under 5, 10 to 14, 40 to 44, and 70 to 74. The excess of incidence in males in these groups is relatively small, and is hardly significant in the highest age groups, where the rates are computed from small figures. Frost found the most striking excess of incidence in females occurring between the ages of fifteen and forty, the difference between the sexes being relatively slight in age periods above and below these limits. Females over the age of fifteen and especially between the ages of 15 and 45 were either more susceptible to infection, or more generally and more intimately exposed than males of corresponding age.

Our own records by the different age groups were remarkably similar. We have found an excess among the females in every age except under five years, 10 to 14, 50 to 54, and 60 to 64. In 1920 we found a slight excess among the males up to the age of 15, and again at the ages 55 to 65. Females predominated in all other ages (Chart XVII). Among those individuals who had attacks of influenza during both epidemics females again predominated except in the ages under 5 years, 10 to 14 and 55 to 59. In our own results we find that ages above 65 show a predominance of females.

After considering both series of results it is safe to generalize in saying that above the age of 15 the female sex tends to acquire the disease in slightly greater proportion than the male sex.

Chart XV shows the predominance of the female incidence in both epidemics.

CHART XVII.

CHART XVIII.

CHART XIX.

CHART XX.

CHART XXI.

Relationship of sex to severity.—In classifying cases as to severity, we have followed the standard previously described. Our results have shown that the 1920 recurrence in our group of individuals has been decidedly milder than the earlier 1918 spread. The proportion of mild cases in 1920 is nearly twice that of mild attacks in 1918–19. The proportion of severe cases was twice as great in 1918 as in 1920. The actual severity in 1918 was even greater than would be indicated by these figures. The last column in Chart XVIII is a combination of the two preceding, and while the 1920 column includes all classed as severe, pneumonia, and fatal, that for 1918 only includes the severe and pneumonia cases, but does not include the fatal cases for that year, because those who died during the 1918–19 epidemics are not counted in our 10,000 individuals surveyed. If these were included the percentage of total severe, or average severity would be greater than 42.70.

We find that in 1918 the female sex had a higher proportion of severe cases according to our standard than did the male. This was equally true in 1920. We should emphasize here that we are not comparing only the fatal cases in the two sexes, but all classified as severe, and including fatal in 1920.

Not only was the female sex attacked in slightly greater proportion, but also the individual cases appear to have been on the aggregate somewhat more severe in that sex.

Morbidity by age.—Before discussing the incidence of influenza in the various age periods we should explain that the charts for 1920 are based on the ages given by the individuals, and those for 1918 upon these ages, corrected by the subtraction of 15 months from the age as given. In our study of cases recurring during both epidemics the age used in the calculations is that of 1920. It is for this reason that in all of our age charts we have a first age period from zero to 15 months. Infants of less than 15 months at the time of our survey were born subsequent to the peak of the 1918–19 epidemic, and are not included in computations for that time.

The general similarity of the age incidence in the six districts studied (Charts XIX and XX) is evident. As a rule two peaks can be discerned, one falling somewhere between 15 months and 9 years, and the other between 20 and 39 years. There are individual variations in the different districts, and in Districts IV, V and VI there is a tendency toward a peak in the period 55 to 64. This, however, disappears when the total 10,000 is tabulated, when the two peaks, 15 months to 9 years, and 20 to 39, show out clearly for the year 1918 (Chart XVII).

Frost found for the same epidemic that the attack rate was highest in the age group 5 to 9, declining with almost unbroken regularity in each successive higher age group, with the exception of the groups 25 to 34, in which the attack rates were higher than in the age groups 15 to 24, but not as high as that of 5 to 9.

Both series of observations agree in finding relatively high incidence in early childhood and in early adult life.

For 1920 (Chart XVII) we find that these peaks, although present, have become decidedly less prominent, and that there is a relatively higher incidence in individuals past the age of 40 (Charts XXI and XXII). There is some tendency toward straightening out of the curve; age appears to have played a less important part, and those higher ages which were relatively insusceptible in 1918 have become more susceptible in 1920. We cannot generalize in the statement that all ages which were lightly attacked in the first epidemic were more severely attacked in the 1920 spread, because the ages from 10 to 19 are found to be relatively lower during both epidemics.

Other observations have been made regarding the age incidence particularly during the 1918 pandemic. Jordan’s figures for the October epidemic show a higher incidence among school children of ages 4–13 than among those of higher school age, 14–18. The teachers in these schools had a lower attack rate than the pupils. The pupils in both school groups were from the same section of the city and to a large extent from the same families and were presumably exposed in similar degree.

Lynch and Cumming found that of 49,140 children in public institutions the influenza rate was 412 per 1,000, while among 703,006 adults in similar institutions the rate was 263 per 1,000. These figures include children in a large number of institutions scattered throughout the United States, and would indicate that in childhood the susceptibility is much greater than in adults.

Many writers agree that nursing infants show a relative insusceptibility. However Abt records a case of an expectant mother who, within two weeks of term, developed influenza, and during the course of her illness gave birth to a baby boy, who at birth was found to be suffering from bronchitis and bronchopneumonia, but who lived for three days, finally dying of bronchopneumonia. Abt concludes from a review of all of the facts that the newly born infant had influenza and that the baby had become infected before birth.

CHART XXII.

According to Carnwath, the age incidence showed curious changes. During the 1918 summer wave the ages most affected were 15 to 45. In the winter of 1918–19 there was a considerable shifting toward the extremes of life and particularly toward the younger years. The susceptibility of young children was the subject of a special inquiry in London. Though the attack rate was below the average, the chances of recovery were less than in other age groups. Of breast-fed infants, 30 per cent. contracted the disease; of artificially-fed 54 per cent. The opposite, however, occurred in lying-in homes. An inquiry in Cheshire revealed that 25.4 per cent. of expectant mothers affected died.

Renon and Mignot have made a report on the 1920 recurrence. According to them the grip of 1920 attacked all ages, in contradistinction to the 1918 epidemic, which attacked especially the young and vigorous. One-third of their group were over 40 years of age, while some were 70 and 80 years old. In spite of this the disease remained relatively mild.

Age morbidity in previous epidemics.—Previous to the epidemic of 1889–93, the various recorded observations regarding morbidity, and particularly regarding age morbidity, have consisted often of records made by practising physicians, and are merely estimates based upon their clinical experience and varying with the type of individual treated by them. Or else they have been records made by non-medical historians. During the 19th century, the tendency toward statistical enumeration becomes more and more prominent, but the first statistical studies of real value to the epidemiologist were made in the epidemic of thirty years ago. Statistical study must begin with this last epidemic. Observations of the earlier epidemics, while very interesting for reference and comparison, are no longer acceptable as unquestioned statements of fact. Even at the present time and with all of the emphasis that is now being laid upon statistical procedure the records are far from perfect, and it is to be hoped that in years to come the improvement will be so decided that the records even of the 1918–20 epidemics will appear crude.

Buoninsegni remarks of the 1387 epidemic that many individuals of all ages died, but the deaths were particularly prevalent among the aged.

Jacob, of Königshofen, writes that “there came a general pestilence in the whole country, with cough and influenza, so that hardly one among ten remained healthy,” and that old and debilitated persons were frequently the victims.

Balioanus tells us that the epidemic of 1404 let not rank, age nor sex escape its effect.

In 1557, according to Valleriola, the disease appeared with pestilential rapidity, and spared neither sex, nor any age, nor rank, neither children nor old persons, rich nor poor, but that it was not as a general rule dangerous; children only, who could not freely cough out the phlegm, dying.

The same story is told by Molineux, for 1693, “All conditions of persons were attacked, those residing in the country as well as those in the city; those who lived in the fresh air and those who kept to their rooms; those who were very strong and hardy were taken in the same manner as the weak and spoiled; men, women and children, persons of all ranks and stations in life, the youngest as well as the oldest.” Molineux, however, added that, “it rather favored the very old who seldom were attacked with it.”

These observations are but broad generalizations; if we pause to study the psychology of the historian we are tempted to conclude that his primary object was to impress his readers with an idea of the enormousness of the dissemination of the disease during his period. That being the main endeavor, a tendency to exaggerate for the sake of rhetoric and yet remain within the limits of truth may be considered excusable. But during the 1889–93 epidemic there was ample opportunity to compare the estimates made by the practising physicians with the later statistical tabulations. As a rule the former were higher both as regards morbidity and mortality.

In the 1830–32 epidemic an interesting observation has been made. While Kahlert says that no distinction between age, sex nor rank occurred, Leberscht stated that persons of middle age, especially women in the climacteric period, were attacked with special frequency. This is of interest in view of the findings in the 1918 epidemic. Krimer states for the same epidemic that children under 14 years of age and adults over 45 years were spared by the epidemic.

For the 1836–37 epidemic Finkler records the following: “Most of the patients were adults from 20 to 40 years of age, and of these more women than men were attacked. Curiously, however, the physicians of Würtenberg speak of the great dissemination of the disease among children.”

In 1847–48, among the adult influenza patients, there are said to have been more women than men. According to Canstatt, there were proportionately more children than adults attacked.

In 1889–90, according to Finkler, no age was spared, but persons between 20 and 50 years of age were attacked by preference. No trade was a sure protection. The course of the disease in general was favorable and also quite rapid, unfavorable only in many children during the first few years of life, in many old people, in many debilitated persons, and especially in those suffering from chest affections.

An interesting table of this kind is given us by Leichtenstern. His hospital material included 439 influenza patients, and these he carefully grouped according to age.

Age. Influenza admissions, General average of per cent. admissions, per cent.

Under 10 years 0.9 0.7

10–20 years 14.7 8.8

20–30 years 40.3 27.5

30–40 years 19.1 23.3

40–50 years 10.1 15.7

50–60 years 7.4 12.3

60–70 years 5.3 8.9

70–80 years 1.7 2.6

Above 80 years 0.4 0.2

Comby found that in Paris only the new-born were noticeably insusceptible to influenza, that children up to 15 years were attacked in the proportion of 40 per cent., and adults in the proportion of 60 per cent. Danchez believed that in families in which all the adults became ill, the little children usually escaped.

Finkler states that in the schools at Bordeaux the older children were first and most frequently attacked. Of the 248 male and female teachers in 41 schools, 153 (61.7 per cent.) developed the disease. Children up to five or six years of age at any rate seem to have been very little affected, while older children were no less susceptible than adults.

Among 47,000 cases of influenza treated by physicians in Bavaria in 1889, the various ages were as follows:

1 year 1.5 per cent. 2–5 5.4 per cent. 6–10 6.6 per cent. 11–15 7.2 per cent. 16–20 11.4 per cent. 21–30 22.2 per cent. 31–40 19.3 per cent. 41–50 12.6 per cent. 51–60 7.7 per cent. 61–70 3.6 per cent. 71–80 2.0 per cent. Above 80 0.5 per cent.

Leubuscher recorded that in Jena the proportion of cases in the individual age classes did not correspond with the figures reported from other localities. Children, and especially very young children, suffered relatively less than adults.

The following statistics of the 1889–90 incidence of influenza among school children in Cologne were collected by Lent:

Attendance. Ill of influenza. Class I–13 to 14 years of age 3,002 1,015 33.8 per cent. Class II–11 to 12 years of age 5,737 1,835 31.9 per cent. Class III–10 years of age 3,701 1,130 30.5 per cent. Class IV– 9 years of age 3,590 930 25.9 per cent. Class V– 8 years of age 2,929 822 28.0 per cent. Class VI– 7 years of age 3,388 758 22.3 per cent.

These may be compared with figures for the public schools in the suburbs of Cologne:

Attendance. Ill of influenza. Class I–13 to 14 years of age 1,609 689 42.9 per cent. Class II–11 to 12 years of age 2,885 1,094 37.9 per cent. Class III–10 years of age 1,683 626 37.1 per cent. Class IV– 9 years of age 1,758 552 31.4 per cent. Class V– 8 years of age 1,771 502 28.2 per cent. Class VI– 7 years of age 1,938 510 26.3 per cent.

The increase of disease incidence with age is apparent. Finkler’s explanation for the higher incidence among the children of the suburbs, “that the children in the country had usually to walk a greater distance to school” does not appear to be complete.

Comby found that out of 3,411 school children in Lausanne 1,840 contracted influenza. This shows a relatively high incidence in children of school age in that city.

Concerning age distribution in 1889–90 Leichtenstern remarks that the greatest morbidity incidence was in school children, adolescents and young adults, especially the last. Nursing infants were attacked in considerably less degree than any of these other ages. Also in the higher ages those above sixty were attacked in lesser degree. The greatest morbidity frequently was between the ages of twenty and forty. Abbott concluded on the basis of estimates furnished him from various institutions and individuals in the State that people of all ages were attacked but the ratio of adults was greatest, of old people next, and of children and infants least.

Relationship of occupation to morbidity incidence.—Leichtenstern found that the only apparent influence of occupation on the incidence of influenza depended upon the liability to exposure in the various occupations. He remarks particularly on the large incidence of influenza among physicians. In contrast was the low incidence in lighthouse keepers. In 1889–90 among 415 dwellers on 51 lightships and 20 isolated lighthouses on the English coast only 8 persons developed influenza and these in four localities, and in every instance there was traceable direct communication from some other source. There is contradictory evidence as to whether individuals working out of doors are more apt to develop influenza. Certain statistics show that postmen and individuals working on railroads were attacked more frequently and earlier than others, while other statistics show that in railroads the office personnel was attacked earlier than individuals on the trains and those working on the tracks.

Abbott concluded that special occupations did not appear to have had a marked effect in modifying the severity of the epidemic. At the Boston Post Office in 1889–90, of the indoor employees, 475 in number, 25 per cent. were attacked. Of the carriers, 450 in number, 11 per cent. were affected with the disease. But there were other reports of the same period which stated that the ratio of the persons employed at outdoor occupations who were attacked was greater than that of indoor occupation.

Finkler has discussed the influence of occupation at some length:

“When we compare the statistics of the last pandemic concerning the influence of vocation, we see in the first place that those first and chiefly were attacked whose occupation compelled them to remain in the open air. This was shown especially by Neidhardt, who studied the influenza epidemic in the Grand Duchy of Hesse. His conclusions, however, were disputed by others. Thus, the prejudicial influence of exposure to the open air was not supported by the statistics of railroad employees in Saxony. Of those who were employed in the outdoor service, 32 per cent. became ill; of those employed in office work, on the other hand, 40 per cent. The statistics of the local benefit societies in Plauen show that the percentage of the sick among farm hands and builders was not greater than that among the members of other benefit societies who worked indoors. In Schwarzenberg the laborers in the forest who were working in the open air all day were affected less than others, and there was no sickness whatever in some forest districts. Lancereaux, of Paris, states that most of the railroad employees who suffered from influenza were those engaged in office work and not those who worked in the open air. The preponderance of influenza patients among the factory hands may be seen from a table prepared by Ripperger:

A. In the open air. Occupation. Per cent. attacked. Workmen and laborers of Niederbayern 7 Railway officials in Amberg 9 Peasants in Niederbayern 11.7 Workmen in the Salzach-Correction 20

B. In closed rooms. Slag mills in St. Jugbert 15 Cotton mill in Bamberg 20 Cotton mill in Bayreuth 33 Sugar factory in Bayreuth 36 Aniline works in Ludwigshafen 38.8 Cotton mill in Zweibrücken 50 Tinware factory in Amberg 60 Factory in Schweinfurth 62 Gun factory in Amberg 70 Gold beaters in Stockach 80

“Many peculiar records of how individual classes of occupation have fared are obviously to be explained by the fact that the infection manifested its action in very different degrees. Thus, among the workmen on the Baltic ship-canal only those became ill who lived in the town of Rendsburg; those who had been housed in barracks outside of the city were not affected. Of the 438 lead workers of Rockhope, which is situated in a lonely valley in Durham, all remained perfectly free from the disease during the three epidemics of 1889–92.

“Some occupations are said to afford protection against influenza. Thus workmen in tanneries, chloride of lime, tar, cement, sulphuric acid, glass, and coke works, are said to have escaped the disease with extraordinary frequency.

“We shall be compelled perhaps to agree with Leichtenstern in his conclusion that occupation and social position only in so far exert an influence on the frequency of the disease as certain occupations in life lead to more or less contact with travellers.

“Very remarkable is the proportionately small number of soldiers affected, at least in the Prussian army, where, according to the official record, the epidemic from its beginning to its end attacked only 101.5 per thousand of the entire forces.”

Comparison of morbidity by occupation necessarily includes so many variables and so many factors other than occupation that the results are decidedly unsatisfactory. An example is found in Jordan, Reed and Fink’s report of the incidence among troops in the Student Army Training Camps in Chicago. They found a strikingly different attack rate in the various groups studied. In the Chicago Telephone Exchange they ranged from 30 to 270 per 1,000, although the working conditions in the various exchanges were not materially different. In the Student Army Training Corps at the University of Chicago the lowest was 39 and the highest 398 per 1,000. The higher rate group was particularly exposed to infection while the lower, although composed of men of similar ages, living under similar conditions, were guarded to a considerable extent against contact with beginning cases.

Woolley has made an interesting observation on the effect of occupation: “The disease was no respecter of persons except that it was more severe in those who were hard workers. Those who tried to ‘buck the game’ and ‘stay with it’ showed the highest mortality rates. So, the non-commissioned officers and the nurses suffered more severely than the commissioned officers and privates.

“The annual morbidity rate per 1,000 was as follows:

For commissioned officers 261 Non-commissioned officers 208 Nurses 416 White enlisted men 568 Black enlisted men 1,130

“The annual mortality rate per 1,000 was:

For commissioned officers 69 Non-commissioned officers 83 Nurses 77 White enlisted men 145 Black enlisted men 253

“The case mortalities were:

Per cent. For commissioned officers 26.8 Non-commissioned officers 40.0 Nurses 33.3 White enlisted men 26.0 Black enlisted men 22.5

“The above figures are for the period of five weeks from August 28th to October 1st, 1918, and cover the most active portion of the epidemic, but are obviously incomplete. They are given for purposes of comparison.”

Woolley makes the observation that the organizations which spent most of the time in the open and which were therefore most exposed to the weather suffered least during the epidemic. This was particularly true in the Remount Depot.

In our work we have attempted to classify our population according to occupation along very broad lines.

“Infant” includes all individuals up to the age of two years. In these the exposure is limited by the fact that they are either relatively isolated at home, or when abroad, are still under relative isolation in a perambulator or under the eye of a nurse. There is relatively little commingling with the older age groups.

“Child,” refers to all children up to the age of school years. There is relatively much greater commingling, particularly with other individuals of the same age.

“School” refers to all children and adolescents who were reported as attending school.

“Home” includes not only the housewife, the housekeeper, but also servants and invalids; all who in their daily routine spend the greater part of the time in the home.

“Manual Indoors” refers chiefly to laborers in factories and includes all manufacturing occupations in which the work is of a manual character no matter what the particular branch.

“Manual Outdoors” refers to such occupations as ditch diggers, street cleaners, conductors and motormen, longshoremen, trucksters and teamsters, telephone and telegraph linemen, etc.

“Retail Sales Indoors” refers to clerks in stores and all other individuals who, working indoors, come into about the same degree of contact with the public-at-large.

“Retail Sales Outdoors” includes sales agents, life insurance agents, traveling salesman, pedlers, newsboys, etc.

“Office,” officials, secretaries, stenographers, telephone operators, telegraph operators, etc.

We have observed that in 1918 infants presented the lowest incidence and school children the highest. Occupations designated Home and Office were surprisingly high. Children also showed a high incidence, one out of every five developing the disease. The records show that manual labor, both indoors and outdoors, was associated with a higher incidence than less strenuous work, as retail sales, indoors and outdoors (Chart XXIII).

The attack rates in most of the occupations are so nearly the same as to lead to no certain conclusions. It would appear from our records that individuals working out of doors were less frequently attacked than those whose occupation kept them in doors. The groups at the two extremes of incidence correspond to what we should expect when considering opportunities for contract. The infant has least direct contact. His contact is only with one or a few individuals, the mother or the nurse. This group developed the disease in 5.8 per cent. The school child not only has the same degree of contact as do adults, but also in the tussle and scramble of play the contact becomes much closer. The factor of age plays a large part in the occupational distribution and the apparent occupational susceptibility is influenced by the age susceptibility.

When we consider the occupational incidence in the various districts we find that the only constant feature in the relatively small groups is the low incidence among infants (Chart XXIV).

CHART XXIII.

CHART XXIV.

CHART XXV.

CHART XXVI.

The first fact gained from a study of the 1920 occupational case rate is that just as was the case in age incidence there is less variation between the highest and the lowest than in 1918–19. While in the first epidemic the highest occupational rate was five times the lowest, in the second it was only twice the lowest (Chart XXV). But at the extremes of the two charts we see some tendency to an inversion of the order. In 1918–19 those occupied in “retail sales” outdoors showed a low incidence, while in 1920 they were the highest. So also, the incidence in the school group changed from highest in 1918 to lowest in 1920. The incidence in infants increased; that in the office workers decreased. No general conclusions are warranted from these results.

In comparing the sex incidence by age groups we have found that females as a rule showed a slightly greater incidence than males. That this is not due fundamentally to occupational differences is suggested by a comparison of the sex incidence in the two epidemics studied. In 1918 the distribution is practically the same in the two sexes in all occupations except “Home,” “Manual Outdoors,” “Retail Sales Indoors,” “Retail Sales Outdoors” (Chart XXVI). In the first the number of males is so small and in the second and fourth the number of females is so small that these cannot justly be compared. The group, “Retail Sales,” consists in 1918–19 of 69 males and 27 females, out of a total distribution in the population of 426 males and 107 females. This is the only occupation that showed a definite higher incidence among the females, and even here the number is too small for accuracy. In 1920 this difference has practically disappeared.

Effect of race stock.—Leichtenstern remarks in his monograph that the reported differences in influenza morbidity among different races, such for instance as European and other nationalities, doubtless are due to factors other than genetic racial differences, such as different modes of living, commerce, etc. The work of the last two years calls for a reconsideration of this idea.

Frost in his valuable work found that “in the seven localities with considerable colored population the incidence rates among the colored were uniformly lower than among the whites, the difference persisting after adjustment of the rate to a uniform basis of sex and age distribution. The extent of the difference varied, being relatively great in Baltimore, Augusta and Louisville, and very small in Little Rock. This relatively low incidence in the colored race is quite contrary to what would have been expected a priori, in view of the fact that the death rate from pneumonia and influenza is normally higher in the colored than in the white, and that the colored population lived generally under conditions presumably more favorable to the spread of contact infection.”

Brewer, in his study of influenza in September, 1918, at Camp Humphreys, finds that the colored troops showed a decidedly lower rate than the white troops throughout the epidemic. He finds that the incidence among colored troops was only 43 per cent. of that among whites. The difference between colored and white organizations was probably not due to difference in housing. Most of the colored troops were in tents and the white troops were all in barracks. But the 42d Company composed of negroes was housed in barracks under the same conditions as the white troops of other organizations and they had next to the lowest incidence of all organizations. Brewer concludes that the colored race when living under good hygienic conditions is not as susceptible to influenza as the white race under the same conditions. The age distribution was the same in both groups.

Armstrong concluded from figures based on reported cases of influenza that in the autumn of 1918 proportionately four times as much influenza and pneumonia was reported among the Italians as was reported for the rest of the Framingham community, made up largely of Irish or Irish-American stock. On the contrary, an examination of a large proportion of the population of that town showed a tuberculosis incidence among the Italian race stock of .48, in contrast to an incidence among the Irish of 4.85 per cent. and of 2.16 per cent. in the entire population. Armstrong contrasts the relative insusceptibility of Italian stock to tuberculosis, with the apparent marked susceptibility to acute disease of the respiratory tract, such as influenza and pneumonia; and the high susceptibility of the Irish to tuberculosis, with their low susceptibility to acute respiratory infection.

With regard to our work it is sufficient to state that the lowest incidence in both epidemics, as well as in recurrent cases, was in the Irish tenement districts. Both the Jewish and the Italian tenement districts were slightly higher in both epidemics (Charts XIX and XXI). The age distribution of the entire population of each of these three districts was about the same, so it does not appear that the slightly lower incidence among the Irish is due to a variation in the age distribution of the population.

The subject of race in relation to influenza will be discussed further under mortality.

MORTALITY.

According to Marchese, in 1387 at Forli in Italy, not a person escaped the disease, but only a few died. Gassar says that during the same epidemic in Germany the patients suffered four, or at most five, days with the most disagreeable catarrhal symptoms and delirium, but recovered, and only very few were removed by death.

Pasquier remarks concerning an epidemic in 1411 that an infinitude of individuals were attacked but that none died.

Concerning the epidemic of 1414 in France, Lobineau relates that the disease was fatal only for the aged. Mezeray also speaks of the high mortality of the old in this epidemic.

Regarding the pandemic of 1510, Thomas Short remarks that none died except some children. Mezeray, on the other hand, says that the disease had claimed many victims.

Pasquier and Valleriola both write of the epidemic of 1557, in France, as being distinctly mild in character. Children only who could not freely cough out the phlegm died. Coyttar speaks of the absence of death except in tuberculous patients.

In the pandemic of 1580 individual observers report enormous death rates. Thus, according to Schenkius, the disease killed 9,000 persons in Rome, while Madrid, Barcelona and other Spanish cities were said to have been nearly depopulated by the disease. This high mortality was, however, even at that time attributed by some physicians to the injudicious employment of venesection. Throughout the more recent history of pandemic influenza opinion seems to have been nearly unanimous that blood letting has had very bad results in the outcome of influenza cases. Remarks to this effect have been made by the contemporaries of nearly every epidemic since 1580.

According to Rayger and others during the epidemic of 1675, nobody died of the disease itself with the exception of debilitated persons, although it spared neither the weak nor the strong.

Concerning the epidemic of 1688, Thomas Short writes for England that though not one of fifteen escaped it, yet not one of a thousand that had it died.

In 1712, Slevogt writes that in Germany “Fear soon vanished when it was seen that although it had spread all over the city, it left the sick with equal rapidity.”

Finkler remarks, concerning 1729–30, that, “The great mortality which attended the epidemic in England and Italy seems somewhat remarkable. Thus Hahn states that in London in the month of September one thousand persons died each week, and in Mayence forty persons daily. Most likely, however, other diseases which were present at the same time added their quota to the mortality, especially as the disease in other places, for example in Germany, ran a benign course.”

Perkins, Huxham, Pelargus, Carl and others, concerning the epidemic of 1732–33, all testify that the disease was of very low fatality.

In 1742 the epidemic was evidenced by an enormous morbidity but the disease was not dangerous as a general rule although Huxham occasionally speaks of the virulent character of the disease in England, and Cohansen says that in January, 1743, over 8,000 persons died from influenza in Rome and 5,000 in Mayence.

We have the testimony of Robert Whytt, for 1758, and that of Razoux and Saillant and Ehrman for 1762, as to the low mortality of the epidemic for those years.

According to Heberden the same was true for 1775, while Webster tells us for 1780 that the disease was not dangerous but its effects were seen the following year in the increased number of cases of phthisis.

Finkler remarks concerning the epidemic of 1802, “The mortality in this epidemic was small, only the abuse of venesection brought many to the grave. Thus, so many farmers are said to have died in Russia from it that venesection was forbidden by an imperial ukase. Jonas says that many patients were bled either on the advice of a simple village barber or by their own wish, and most of them died. In Prussia also bleeding was declared detrimental by the Government.”

He continues regarding 1836–37, that, “In London there died, during the week ending January 24, 1837, a total of 871 persons, and among these deaths there were 295 from disease of the respiratory organs; during the week ending January 31st, out of a total of 860 deaths there were 309 from diseases of the respiratory organs.”

Watson, in describing the epidemic of 1847, discusses the mortality:

“The absolute mortality has been enormous; yet the relative mortality has been small. You will hear people comparing the ravages of the influenza with those of the cholera, and inferring that the latter is the less dangerous complaint of the two; but this is plainly a great misapprehension. Less dangerous to the community at large (in this country at least) it certainly has been; but infinitely more dangerous to the individuals attacked by it. More persons have died of the influenza in the present year than died of the cholera when it raged in 1832; but then a vastly greater number have been affected with the one disease than with the other. I suppose that nearly one-half of those who were seized with the cholera perished; while but a very small fraction, indeed, not more probably than two per cent. of those who suffered influenza have sunk under it.”

Leichtenstern remarks on the very low mortality of 1889–90. In Munich 0.6 per cent. died; in Rostock 0.8 per cent.; in Leipzig 0.5 per cent.; in fifteen Swiss cities 0.1 per cent.; in Karlsruhe 0.075 per cent.; in Mecklenburg-Schwerin 1.2 per cent. This does not, however, include the numerous deaths from complications, as from pneumonia, and does not express the true mortality.

Newsholme gives the following table for mortality from influenza, bronchitis and pneumonia, in England and Wales during the epidemic years and the years immediately preceding them. The figures express annual death rate per million of population. The highest rate was reached in 1891. The table does not include deaths registered as from other diseases, but due directly or indirectly to influenza. Respiratory diseases in general show a greatly increased death rate in years in which influenza is epidemic. Such is also true to some extent with diseases of the nervous and the circulatory systems.

═══════════╤═════════════════════════════╤═════════════════════════════ Death rate │ │ per million│ │ of │ Non-epidemic years. │ Epidemic years. population │ │ from │ │ ───────────┼─────────┬─────────┬─────────┼─────────┬─────────┬───────── „ │ 1887│ 1888│ 1889│ 1890│ 1891│ 1892 ───────────┼─────────┼─────────┼─────────┼─────────┼─────────┼───────── Influenza │ 3│ 3│ 2│ 157│ 574│ 533 Bronchitis │ 2,117│ 2,041│ 1,957│ 2,333│ 2,593│ 2,266 Pneumonia │ 1,113│ 1,093│ 1,022│ 1,404│ 1,471│ 1,250 ───────────┴─────────┴─────────┴─────────┴─────────┴─────────┴─────────

In a report by the United States Public Health Service early in 1919 the death rates from all causes in twelve large cities of this country were compared for 1889–90 and for 1918–19. It was found that while considerable irregularity in the curves was evident, the curves of the two epidemics manifested on the whole quite a striking similarity for the same cities considered individually and for the group as a whole. The death rate rose to a much higher point during the autumn wave of the 1918 epidemic than in the epidemic of 1889–90 in nine out of the twelve cities. During both epidemics the rate was relatively low in St. Louis, Milwaukee and Minneapolis. The mortality in all of these cities was 26.7 in 1889, as against 35.2 for 1918. In the peak week the rate rose to 55.6 in 1918 as against 35.4 in 1889.

The influenza deaths in Massachusetts in the year 1890 during a period of fifty days were estimated by Abbott to have been 2,500. In 1918 Jordan estimates the mortality for the same state to have been six times as great. The population of the state had not doubled in the interval. The highest mortality from influenza in Massachusetts during the 1889–93 epidemic occurred in January, 1892, during which month the total deaths amounted to 6,309 which was greater by 2,246 than the mean monthly mortality of the year, and greater by more than 1,000 than the mortality of any month in the ten year period 1883–92.

A comprehensive comparison of the damage done by influenza in 1918 with the deaths from other plagues has been made by Vaughan and Palmer.

“The pandemic of 1918, when compared with that of 1889–90 is estimated to have caused six times as many deaths.

“During the four autumn months of 1918, 338,343 cases of influenza were reported to the Surgeon General. This means that in the camps of this country one out of every four men had influenza.

“The combination between influenza and pneumonia during the fall of 1918 seems to have been closer and more destructive than in any previous pandemic. During the autumn season there were reported to the Surgeon General 61,691 cases of pneumonia. This means that one out of every twenty-four men encamped in this country had pneumonia.

“During the same period 22,186 men were reported to have died from the combined effects of influenza and pneumonia. This means that among the troops in this country one out of every sixty-seven died.

“This fatality has been unparallelled in recent times. The influenza epidemic of 1918 ranks well up with the epidemics famous in history. Epidemiologists have regarded the dissemination of cholera from the Broad Street Well in London as a catastrophe. The typhoid epidemic of Plymouth, Pa., of 1885, is another illustration of the damage that can be done by epidemic disease once let loose. Yet the accompanying table shows that the fatality from influenza and pneumonia at Camp Sherman was greater than either of these. Compared with epidemics for which we have fairly accurate statistics the death rate at Camp Sherman in the fall of 1918 is surpassed only by that of plague in London in 1665 and that of yellow fever in Philadelphia in 1793.

“The plague killed 14 per cent. of London’s population in seven months’ time. Yellow fever destroyed 10 per cent. of the population of Philadelphia in four months. In seven weeks influenza and pneumonia killed 3.1 per cent. of the strength at Camp Sherman. If we consider the time factor, these three instances are not unlike in their lethality. The plague killed 2 per cent. of the population in a month, yellow fever 2.5 per cent. and influenza and pneumonia 1.9 per cent.

“In four months typhoid fever killed 1.5 per cent. of the soldiers encamped in this country during the war with Spain. Influenza and pneumonia killed 1.4 per cent. of the soldiers in our camps in 1918 and it also covered a period of four months.”

The Bureau of the Census has made the following report concerning influenza deaths in the United States:

“In forty-six American cities, having a combined population of only a little more than one-fifth the total for the country, the mortality resulting from the influenza epidemic during the nine weeks period ended November 9th was nearly double that in the A. E. F. from the time the first contingent landed in France until the cessation of hostilities.”

The mortality, even as the morbidity, has varied in different localities and at different periods. The low morbidity and mortality in the spring of 1918 has been frequently mentioned. Among the Esquimaux in Alaska the death toll was terrific. Whole villages of Esquimaux lost their entire adult population. It has been estimated that in British India the death roll totalled 5,000,000. “The central, northern and western portions of India were the worst sufferers. The hospitals in the Punjab were choked so that it was impossible to move the dead quickly enough to make room for the dying. The streets and lanes of the cities were littered with dead and dying people. The postal and telegraph services were completely disorganized; the train service continued, but at all principal stations dead and dying people were being removed from the trains. The burning ghats and burial grounds were literally swamped with corpses, while an even greater number awaited removal. The depleted medical service, itself sorely stricken by the epidemic, was incapable of dealing with more than a minute fraction of the sickness requiring attention. Nearly every household was lamenting death, and everywhere terror and confusion reigned. No part of the Punjab escaped.”

The Bureau of the Census estimates that 445,000 deaths from the epidemic of influenza occurred in the United States in the period between September 1st and December 31st, 1918. There is no doubt but that the total death toll for that epidemic exceeded 500,000 individuals.

According to Winslow and Rogers, the two highest annual death rates on record in Connecticut are both rates of 19.4 per 1,000 and these two rates are for the influenza epidemic years of 1892 and 1918. In the earlier of these two the normal general death rate was several points higher than it is today, so that the effect of the recent epidemic was much more serious than was that of its predecessor. For a single month the death toll of October, 1918, was absolutely unprecedented in Connecticut. They estimate that the epidemic between September, 1918, and January, 1919, cost the State 5.5 lives per 1,000 population, or, in all, 7,700 lives.

In the United States Army there was a total of 688,869 admissions for influenza. The total deaths ascribed to the disease are 39,731, which gives a rate of 15.64 per 1,000 for the acute respiratory diseases out of the total disease death rate of 18.81 for the year. In 1915 the per cent. of deaths from this group of infections was under 18 per cent. of the total from all diseases. During the last four months of 1918, 11,670 deaths from influenza and pneumonia occurred in the American Expeditionary Forces in France. There were approximately 1,600,000 officers and men in the United States and an equal number in France.

Carnwath gives the following comparison of the number of deaths in London and in certain American cities from influenza and all forms of pneumonia during the eight weeks of the 1918–19 epidemic.

Deaths in London and in American cities. Number of deaths. Rate eight weeks per 100,000 of population.

London 13,744 341

New York 20,681 360

Chicago 8,785 343

Philadelphia 12,806 749

Boston 4,211 548

The cause of death in the vast majority of cases is some form of pneumonia. In fact it has been questioned whether influenza uncomplicated can cause a fatal issue. Postinfluenzal meningitis has been the cause of death in an appreciable number of cases. More remotely the disease has caused many deaths by hastening the fatal outcome of what were otherwise subacute or chronic conditions of the respiratory, cardiovascular, or renal systems.

Vaughan and Palmer record that, “The pandemic of influenza in 1918 seems to have been more closely associated with the pneumonias than appears in any previous pandemic. From the reports as sent to the Surgeon General’s Office, it appears that uncomplicated influenza was not by any means a fatal disease and that the high death rate was due to the pneumonias which followed. Pneumonia is a serious disease at all times. Recent records for the United States Army show that the case mortality rate for this disease has been as follows during the different periods of the last two years:

Per cent. The year 1917 11.2 6 winter months, 1917–18 23.1 5 summer months, 1918 18.8 4 autumn months, 1918 (Influenza period) 34.4

“It is not strange that once pneumonia has secured a foothold in patients already weakened by influenza their chances of recovery were lessened.”

Woolley reports that for the troops stationed at Camp Devens, Mass. there were no fatalities from uncomplicated influenza. In every fatal case but two a diagnosis of pneumonia was made, and in these two cases pure cultures of pneumococcus were obtained from the blood after death, so it appears that they were cases of pneumococcus septicemia. Up to October 29, 1918, 19 per cent. of the total number of influenza cases reported developed pneumonia and of these there was a case mortality of 27.9 per cent. The mortality rate among the influenza cases was 5.4 per cent.

At Camp Humphreys, Virginia, 16 per cent. of the camp was attacked by the disease; 28 per cent. of influenza cases had pneumonia; 10 per cent. of influenza cases died; and 35 per cent. of pneumonia cases died. One and six tenths per cent. of the population of the camp died from influenza. The camp had an average strength of 26,600 individuals. Fifty-two per cent. of the entire number of cases occurred during the peak week which ended October 4th.

Between September 21st and October 18th, 1918, 9,037 patients were admitted to the Base Hospital at Camp Grant. This represented about one-fourth of the strength of the camp. Of these 26 per cent. developed pneumonia and 43 per cent. of the pneumonia cases died. Death occurred to about 11 per cent. of the total admissions.

The death rate at Camps Devens, Sherman and Grant were among the highest of all of the camps in this country. The annual death rate from all causes per 1,000 for the four last months of 1918 were 132 for Camp Cody, 123 for Syracuse, 116 for Camp Sherman, 102 for Camp Beauregard, 97.3 for Camp Grant, 75.0 for Camp Dix, 67.0 for Camp Devens. These seven camps stood out high above the majority. By far the majority, 28 camps, had an annual rate between 61.9 and 25.5 per 1,000. Only four camps recorded lower rates than the latter figure.

The Municipal Statistics of Paris showed that during the first half of October, 1918, the average weekly mortality was from two to three times that of nonepidemic years. The returns for the Departments of France also showed a mortality three times above the average for previous years, though not uniformly so. In the Departments the mortality from influenza did not exceed 10 per cent. and in many cases it was below 5 per cent. On the other hand cases admitted to hospital, which consisted of the worst forms of the disease, showed a mortality varying between 12 and 30 per cent. Returns received from Italy were similar. The disease in that country was especially severe in the northern part and in the provinces bordering on Switzerland. Marcus, of Stockholm, reported in September, 1918, that the epidemic in Sweden was running a very severe course, more than 1,000 deaths having occurred up to the time of his report. According to Weber, 2,770 deaths occurred in Berlin during October, 1918, from influenza and pneumonia alone. In Vienna there died from influenza between September 1st and October 19th, 1918, 3,125 persons. The deaths in Vienna from influenza and pneumonia normally total 40 to 50 per week. At the highest point of the epidemic this number had increased to 1,468. Böhm estimates the total influenza incidence in Vienna as 180,000 cases, with a probable mortality around 1.7 per cent. Dunlop estimates that the total number of influenza deaths in Scotland in the winter of 1918–19 may be assessed at 20,000.

A. Giltay has compared the epidemics of 1890 and 1900 with that of 1918 as regards mortality, in Amsterdam. He has studied figures for seven consecutive weeks in each of the three periods under observation and found that the maximum figures for mortality were 61.5 in 1890, 41.2 in 1900, and 52.7 in 1918, but if these figures are compared with the average mortality for the year it is found that the increase of mortality as the result of influenza alone is 39.3 for 1890, 24.5 for 1900, and 40.3 for 1918. Thus the present epidemic is more severe than that of 1890.

Many reported mortality figures are without value because they are either death rates in selected groups such as those in a hospital, or, because the report does not state the status of the individual. Thus, Hoppe-Seyler stated at a meeting of the Kiel Medical Society that of 577 cases treated in the Municipal Hospital, nearly all of which were severe, 28.9 per cent. died. This was reduced to 18 per cent. after deducting the cases admitted in a moribund condition. Again, Rondopoulos reports that the October wave in Greece resulted in a mortality of from 15 to 24 per cent, in different localities.

Just as current vital statistics are of little value in determining the morbidity rate, so also they cannot be relied upon in obtaining fatality percentages. In organizations such as the Army, where all cases are reported, we may get some idea of the fatality rate. The deaths in the United States Army have already been discussed. Marcus, of Stockholm, reports that the military records showed that there had been 34,000 cases in the Swedish Army, with 444 deaths, making a mortality of 1.3 per cent, in that Army.

House surveys also give a fair idea of the mortality. Winslow and Rogers conclude that the fatality rate was as a rule somewhere between two and four deaths per 100 cases, the lower being more likely to be correct. Reeks found in his house census that there had been 3.9 deaths per 100 cases in the autumn of 1918. Carnwath reports that Dr. Niven, in his census, discovered that out of 1,108 cases in the spring and autumn of 1918 there were but 15 deaths, which would give a fatality rate of 1.3 per 100 cases.

Frost has found from his large survey that the ratio of deaths to total cases of influenza varied in the localities surveyed from 3.1 per cent. in New London as a high point to 2.8 per cent. in San Antonio, Texas. There was some apparent relationship between fatality rate and geographic distribution, the higher rates being in San Francisco on the Pacific Coast, and in the localities studied on the north half of the Atlantic Seaboard, and the lower rates being in the central and southern states. The fatality rate on the Pacific Coast was 2.33, on the Atlantic Seaboard 2.05, and in the last district 1.08 per cent.

Our own figures correspond very closely with those of Frost. Among the 10,000 living individuals surveyed in 1920 there were 1,970 cases of influenza in 1918. Add to this the 50 deaths for 1918, which were not included in the 10,000 living individuals, which makes a total incidence of 2,021. This case fatality rate of 2.47 per 100, corresponds closely to Frost’s rate for the North Atlantic Seaboard.

The relative mildness of the 1920 recurrence is indicated in the lower case fatality rate. Fourteen out of 955 cases died, giving a rate of 1.47 per 100 cases.

Mortality by sex.—There is not a uniformity of opinion as to which sex suffered the higher fatality rate during the 1918–19 spread. Winslow and Rogers found for Connecticut a distinctly heavier mortality among males for the last four months of 1918, 58 per cent. of the influenza-pneumonia deaths being among this sex. They believe that this is probably due to a greater exposure to the original infection.

Fränkel and Dublin point out that in a study of 70,729 policy holders of the Industrial Department of the Metropolitan Life Insurance Company in the period from October 1, 1918, to June, 1919, the death rates for males and females were practically the same for both white and colored individuals.

The excess of males over females among the whites is only three per cent., and there was no excess among colored. In contrast, the respiratory diseases, including influenza-pneumonia, under normal conditions, show a higher mortality incidence among males than among females. In the seven year period from 1911 to 1917 the mortality rate showed an excess of 18 per cent. males over females, among whites, and of 30 per cent. among colored. This would seem to indicate that the effect of the epidemic was not much, if any, greater on males than on females, and suggests that the excess mortality caused by the epidemic did not operate on the sexes as the normal mortality from influenza-pneumonia had in previous years.

Dunlop finds that in a study of 10,797 deaths registered in Scotland up until the end of December, 1918, 52.44 per cent. were females and 47.56 were males. These were for deaths reported as due only to influenza. Apert and Flipo found a decided predominance among the female deaths in Paris. In both of these observations the absence from the civilian population of male inhabitants of military age obscured correct comparative statistics.

Once again, Frost gives the most comprehensive discussion of the subject. He found, as we have stated, that the influenza case incidence in persons over fifteen years of age was higher in females than in males, and that in persons under fifteen the relative incidence as between males and females is variable, but with very slight excess in males for the localities studied, combined. On the other hand, the case fatality, the per cent. of influenza cases dying, under fifteen years of age, was higher in females than in males. Over sixty years of age it was considerably higher among the females, but between the ages of fifteen and sixty the general tendency was to a much higher case fatality among the males. The difference was greatest between the ages of 20 and 40. The case fatality between the ages of 15 and 45 in the group of southern and central states was in decided contrast to that in the Northern Atlantic and Pacific groups, the case fatality in the former being remarkably low in both sections and slightly higher in females than in males. He suggests that in the south and middle west where the epidemic was generally milder in respect to mortality than in the northeast and far west, the essential difference was not in case incidence, but in case fatality, especially in persons from 15 to 45 years of age, and in the relatively low case fatality among young male adults. Frost makes the important point that the relative mortality is determined more accurately by case fatality than by case incidence, and that without a full and exact knowledge of the variations in case fatality, statistics of mortality are by no means translatable to terms of relative morbidity. The fact that certain cities showed, as described by Pearl, relatively high mortality rates, does not give conclusive evidence that the morbidity was higher in these cities than elsewhere. The lower influenza case fatality in females from 15 to 60 years of age appears to be accounted for in part at least: first, by a decreased incidence of pneumonia as compared with the males; and, second, by a lower fatality in those cases which did develop pneumonia.

The relatively small number of fatalities in our own records do not warrant a classification by age groups. We found that for all ages in 1918 7.9 per cent. of females developed pneumonia as contrasted with 6.8 per cent. males. This does not include those who died. In 1920, 1.87 per cent. of the male cases died, while only 0.37 per cent. of the females died. Five and fifteen-hundredths per cent. of all male cases developed pneumonia and recovered, and 3.56 of the females did likewise. In 1920 a higher proportion of males than females developed pneumonia, and likewise a higher proportion died.

Relationship of age.—Leichtenstern has summarized the results for the epidemic of thirty years ago, in saying that the death rate for children under one year was little disturbed by the influenza epidemic; that there was very little increase in mortality in the other ages of childhood; that the higher age periods showed the greatest relative mortality for the disease. On the contrary, the records for England and for Switzerland showed during those periods a higher death rate in children up to five years of age.

Percentages. Ages. 1847–8 1890 1–5 10.5 5.2 5–20 13.1 4.3 20–40 3.8 4.7 40–60 18.5 36.2 60–80 16.9 22.4 Above 80 8.6 2.5

Giltay has compared the age mortality in Amsterdam in 1890, 1900 and 1918 as shown in the following table:

═══════╤═══════╤═══════╤═══════╤═══════╤═══════╤═══════╤═══════╤═══════ │ Under │ │ │ │ │ │ │ │ one │ 1–4 │ 5–13 │ 14–19 │ 20–49 │ 50–64 │Over 64│Total. │ year. │ │ │ │ │ │ │ ───────┼───────┼───────┼───────┼───────┼───────┼───────┼───────┼─────── 1890│ 8.4│ 8.1│ 2.3│ 3.0│ 30.7│ 19.3│ 28.1│ 100 1900│ 9.7│ 8.8│ 1.6│ 3.2│ 17.6│ 18.3│ 40.8│ 100 1918│ 3.0│ 13.0│ 8.7│ 8.3│ 51.9│ 8.7│ 6.4│ 100 ───────┴───────┴───────┴───────┴───────┴───────┴───────┴───────┴───────

Evans has studied the records for the city of Chicago in the epidemic of the year 1890, and found that the number of deaths was highest among persons from 20 to 40 years of age. The greater increase above the expected was in deaths of persons over 60 years of age. Children of school age seemed to enjoy some relative immunity, as shown in the mortality reports.

This latter age grouping for 30 years ago corresponds with those of 1918. Frost found that the death rate per 1,000 was notably high in children under one year of age, in adults from 20 to 40, and in persons over 60. The case fatality from pneumonia in his series tended to be fairly constant, around 30 per cent., except in San Antonio, Texas, where it was only 18.5 per cent. Case fatality was also higher in the following age groups: Under one year, 20 to 40, and over sixty.

This age distribution was probably the same in all countries. Filtzos, describing the epidemic in Greece, said that the ages that suffered most and had the most fatal cases were between 20 and 45. In Spain in May and June of 1918 the mortality was much lower among children and the aged than it was among the adults, especially between 20 and 39 years of age. The disease appeared fatal almost exclusively in these ages. In Vienna, 29.5 per cent. of all the fatal cases were between the ages of 20 and 30. Hoppe-Seyler stated that the ages of most of the cases were between 20 and 40 and the majority between 30 and 40, but that the mortality was highest among the older patients.

Dunlop found that in Scotland the most frequent ages at death were between 25 and 35, 25.28 per cent. of the total being between these two ages. 53.85 per cent. of the total deaths were between 15 and 45 years. The highest age group death rates occurred in age groups 75 and over, and 25 to 35, the former being 7.87 per 1,000, and the latter 7.12. High rates also occurred in age groups under one, and 65 to 75, the former being 6.49, and the latter 5.33. The lowest age group death rates were found in the groups which included children of school age, 5 to 15, being 2.20 per cent., and the age group 10 to 15, being 1.80 per cent. Dunlop has apparently only included those cases in which influenza was diagnosed as the cause of death, and has omitted all in which the diagnosis was bronchitis or pneumonia.

The Bureau of the Census has issued a report based on the mortality in Indiana, Kansas and Philadelphia, for the period September 1st to December 31st, 1918. It shows that the highest rate occurred in the age period from 30 to 34 years, with the period from 25 to 29 second. Of all the deaths tabulated more than half occurred between the period of 20 to 40, although this age group represents only 33 per cent. of the total population concerned.

Age mortality has been studied thoroughly by Winslow and Rogers in Connecticut:

“The four last months of 1917 show a normal age distribution with one quarter of all deaths occurring under five years of age, one quarter between 5 and 40 years, and one-half over 40 years, the proportion of the infant deaths decreasing and the proportion of deaths in old age increasing as one passes from the season of intestinal disturbances to the season of respiratory diseases. In 1918 the distribution of deaths from all causes is strikingly different. Instead of less than a quarter of all deaths occurring between the ages of 5 and 40 years, this period included 49 per cent. of all deaths in 1918; and the two decades between 20 and 40 included 40 per cent. of all deaths (as against only 14 per cent. in 1917).

“Considering influenza and pneumonia alone, these two decades included 56 per cent. of the deaths, while only nine per cent. occurred at ages over 49. The decade between 20 and 29 was most severely affected, including 30 per cent. of all deaths, while the decade between 30 and 39 was a close second with 26 per cent. An even higher incidence occurred at ages under five years, as has been brought out in other investigations, since this age period contributed 16 per cent. of all the influenza-pneumonia deaths. The proportion of deaths from all causes in infancy did not rise even to normal, but with the enormous rise in total deaths the maintenance of a nearly normal ratio, of course, means a heavy influenza mortality.”

Jordan observes in his analysis a low pneumonia incidence among the pupils of elementary and high schools. There were no deaths in 188 cases.

Wollstein and Goldbloom report that in a series of 36 children with influenza and bronchopneumonia at the Babies Hospital in the City of New York, 66.6 per cent. died. Achard and his co-workers review a similar series of 32 infants in Paris with influenza. Eight of the 32 died. In both of these studies we are dealing with selected groups of hospital cases and the mortality rates are of little value for this type of study.

Fränkel and Dublin in a study of 70,729 deaths from influenza-pneumonia among the policyholders of the Industrial Department of the Metropolitan Life Insurance Company, find that during the normal period between 1911 and 1917, influenza-pneumonia attacked primarily the first age period of life, ages one to four years, and the period of late middle life and old age. The rates are normally minimal between 5 and 30 years. In the last quarter of 1918, on the other hand, the highest rate among the whites is in the period of early adult life, between the ages of 25 and 34. There appear three modal points instead of the two at the extremes. They find that the excess over normal was most marked in infancy and early childhood, and particularly in early adult life, culminating between the ages of 25 and 34. The period of old age shows no significant excess during the period of the epidemic.

If the deaths among the white males of the age period of active adult life had continued throughout the whole year as they did during the last quarter of 1918, approximately four per cent. of the population of that age would have died.

Fränkel and Dublin are of the opinion that this change in the age incidence of influenza mortality between epidemic and endemic periods suggests strongly that the two diseases are different; that endemic influenza is not the same disease as epidemic influenza. Or perhaps they should say more correctly that the diseases occurring in interepidemic times which are reported to them as deaths due to influenza-pneumonia are not the same as the epidemic influenza. They draw similar conclusions from the different manner in which the white and black races are affected during the interepidemic and epidemic periods, from so-called influenza-pneumonia. We have seen from Frost’s results that it is hazardous to compare mortality rates of different localities and different times with the idea of comparing the disease, influenza, itself.

The ages showing highest mortality in the autumn of 1918 appear to have been essentially the same as those which predominated thirty years ago. There appears to be nothing in the age distribution that could be explained by an immunity persisting over from the epidemic of 1889–93. The age group 30 to 40 has almost universally a higher mortality than the groups below 20, which would by this theory be non-immune and would be expected to have a higher rate. The drop in rate is nearer the age group of 40 than 30. The presence of smaller or larger influenza epidemics in the course of the thirty years would further complicate such an hypothesis.

Relationship to occupation.—Dublin found in a study of 4,700 miners that the death rate was unusually high from influenza in these individuals for the last quarter of 1918. In fact in the age period 45 to 65 the rate among bituminous coal miners is close to four times as high as among all occupied males. The annual death rate per thousand for all ages among the former is 50.1; among all industrial white males, 22.3. The increase is apparent in all age groups from 15 to 65 inclusive. These results are based on the records of the Metropolitan Life Insurance Company.

Density of population. Rural and urban environment.—There have been few reports which have like the above described clearly variations due apparently only to occupational differences. Some attention has been paid to a comparison of the rural incidence with that in large cities. Although other factors play a part here, we may consider this under the general subject of occupation. Statistics for the fall of 1918 from the Netherlands show that with the exception of men over 80 years of age the mortality was remarkably increased for both sexes in communities of less than 20,000 inhabitants.

Winslow and Rogers have studied the variations in the urban and rural incidence and find that in Connecticut with the single exception of Tolland County, in which the small towns were severely hit, the rates were in every case higher in the large communities. In New Haven County, for instance, among nine towns which were purely agricultural, the combined death rate from influenza and pneumonia for the three months of September to November, inclusive, was 9.2 on an annual basis. For six towns in the same county in which there were manufacturing plants the corresponding rate was 15.6. In Litchfield County the twelve purely agricultural towns had a combined rate of 6.5, whereas among eleven partly manufacturing towns the rate was 18.3. This was true for other counties. The figures quoted are for influenza-pneumonia rates only up to December 1st, but study of the records during the early months of 1919 did not show any change in the figures. The rates for the entire state for January, 1919, was 19.8, and that for the towns under 5,000, only 17.5.

These observations differ somewhat from those reported by Pearl, who studied 39 large cities of the United States in an attempt to find a correlation between the explosiveness of the influenza outbreak and the density of population. He concluded that there was no such correlation. Pearl, however, was dealing with cities which were all sufficiently large to offer practically complete opportunities for contact infection, and the two reports, therefore, cannot be justly compared. Winslow and Rogers suggest as possible causes for lessened incidence in rural communities either diminished opportunities for contact infection or differences in age distribution and racial composition of the different populations.

Let us consider in greater detail the fate of both rural and urban individuals who had been recently drafted into the military forces of this country. Almost universally the raw recruit was found more susceptible to disease than was the seasoned soldier. A report by Lieutenant W. D. Wallis from Camp Lee “shows that while those who had been in the service less than one month constituted only 9.19 per cent. of the total strength, they furnished 30.11 per cent. of the total deaths from influenza and consequent pneumonia. Furthermore, it is shown that while those who had been in the service from one to three months constituted 45.18 per cent. of the camp, they furnished 46.24 per cent. of deaths. On the other hand, those who had been in the service more than three months constituted 46.63 per cent. of the population and furnished only 23.69 per cent. of deaths.

Lieutenant Wallis says: “These figures show a much greater percentage of deaths for the first month in camp than the corresponding proportion of the population would warrant; while in the period of three months or more of service the percentage is less than half of that of the camp population having this length of service. The only approach to a correspondence is in the period from one to three months where the respective percentages differ but little. The increase in length of service is accompanied by a progressive decrease in the percentage of deaths from 30.11 per cent. to 27.41 per cent. to 18.87 per cent., although only 9.19 per cent. of the population in the camp falls within the class of less than one month’s service.

“The incidence of mortality is in the first month’s service more than three-fold the percentage of the number of men; and in the period of three months or more of service is scarcely more than half of the percentage of the number of men of the camp in that group.

“The fact that the case mortality is higher among those who came from rural homes than among those who came from cities seems to hold even after three month’s of service, or more.”

Vaughan and Palmer found that the case fatality at Camp Dix among those who came from cities with a population of 10,000 or more was 10.8; while among those who came from more rural homes the rate was 15.8, although the average service of both groups was the same.

The Camp Surgeon of Camp Grant concluded from his records that the new recruit is more susceptible to influenza and is more apt to succumb than is the man who has been trained and is accustomed to Army life.

Wooley reports data collected from four Infantry organizations at Camp Devens comprising 15,502 men. Of 9,559 men who had been in camp less than five months, 3,575 or 37.5 per cent. developed influenza, whereas of 5,943 men who had seen more than five months service in the army, 1,033 or 17.5 per cent. developed the disease. He concludes that the large number of recruits in the camp certainly was a factor in increasing the disease incidence. It should be remarked that Camp Devens appears not to have had any influenza epidemic in the spring of 1918.

It is to be regretted that we have not several reports dealing with the same subject from camps where the disease was definitely recognized in the spring. Fortunately we have one such. Opie and his co-workers have observed that the epidemic at Camp Funston, which occurred between March 4th and March 29th, 1918, and which attacked 1,127 out of a total of 29,000 men, involved chiefly the organizations which had been at Camp Funston during six months or more. At that time it seems to have infected all susceptible individuals, and to have spent itself. Subsequent waves of influenza, four in number, and coming at a little less than one month intervals, occurred when newly drafted men were brought into the camp in April and May. In these latter cases the disease affected the men newly arrived in camp.

At Camp Funston, at least, the higher incidence in the raw recruit appears to be explained in part by a relative immunity of those who had been in camp a month or more, existing as a result of an earlier prevalence of the disease. More abundant evidence would, however, be necessary before we could deny a diminution of natural immunity in the recruits, caused by the exposure, overwork, fatigue, and change of daily routine. As V. C. Vaughan has remarked: “It appears that natural immunity gives way before exposure, overwork and fatigue, as was demonstrated years ago by Pasteur in his experiments on birds with anthrax. Likewise, it is possible for human beings to have their resistance lowered by exposure to unaccustomed environment, so that although naturally immune, the standard of immunity is reduced to the point where the influenza virus gains admittance and overcomes the lowered resistance.”

Race stock and mortality.—The relationship of morbidity to race stock has already been considered and should be borne in mind in a discussion of mortality by race.

We have seen how the natives of India suffered unusually from the influenza, the total deaths being estimated at over 5,000,000 individuals. A preliminary report from the Department of the Interior on the mortality from influenza among American Indians showed that during the six months period from October 1, 1918, to March 31, 1919, over two per cent. of the Indian population died of influenza. The mortality among Indians in the Mountain States, especially in Colorado, Utah and New Mexico, was very high. For the Indian population as a whole the annual mortality rate from influenza alone during the six months period was according to the U. S. Public Health Reports 41.2 per 1,000, which is above that for the larger cities in the United States during the same epidemic period.

In both of the above races we cannot say that it was not factors other than race, particularly living conditions, that resulted in the high mortality.

Winslow and Rogers found in Connecticut that the proportion of influenza-pneumonia deaths was lower than would be expected among persons of native Irish, English and German stock, but higher than would be expected among Russian, Austrian, Canadian and Polish stock, and enormously high among Italians. They suggest that this marked difference in racial incidence may be very largely due to the differences in age distribution of the various race stocks, the races showing the highest ratios being those which have arrived more recently in the country and which are made up more largely of young adults at the ages which suffer most severely from influenza. They further refer to the work done by Armstrong in Framingham, and state that their results tend to confirm his conclusions in regard to the Italians, as do the figures presented by Greenberg from the records of the Visiting Nurse Association of New Haven. “It appears that Italy suffered very severely from the influenza epidemic in Europe, and Dublin has shown that the normal pneumonia rate of this race is a very high one.”

We have rather more abundant comparison of the white and black races in this country. Frost found in his extensive survey that the case fatality was generally higher among the colored than among the white population. A similar observation was made by Howard and Love, who found that the case mortality for influenza and its complications in the United States and in the American Expeditionary Forces, in 1918, was for colored troops 4.3 per cent. and for white troops 3.3.

These two series of observations are of great importance, for they are about all we have describing case fatality rate. The majority of other reports describe mortality rate only, and are therefore not complete.

The death rate in the Army was higher among colored troops, but the incidence of influenza, the rate per 1,000, was lower for the colored race. “Considering only the southern states, the nativity rate for influenza for the white was 247.11 and for the colored, 154.58. For lobar pneumonia it was 10.77 for the white and 28.31 for the colored; for bronchopneumonia and unclassified pneumonia 7.26 for the whites and 11.43 for the colored. It seems probable that the negro is less susceptible to influenza than the southern whites, but that he is much more susceptible to pneumonic infections, either primary or secondary.”

Fränkel and Dublin have studied the racial distribution of 70,729 deaths among policy holders of the Industrial Department of the Metropolitan Life Insurance Company, particularly with respect to incidence among white and black. Normally the mortality from respiratory diseases is higher among colored persons than among whites. In the seven year period from 1911 to 1917, influenza-pneumonia death rates showed an excess of 72 per cent. colored males over white males and of 56 per cent. colored females over white females. During the period of the epidemic the situation was reversed. The whites suffered from higher rates than the colored. While the rate among white males during the period, October to December, 1918, was nearly fifteen times as great as during the period 1911 to 1917; that of colored males was only seven times as great as the rate during the same seven year period. White females during the height of the epidemic showed a rate more than sixteen times as high as the normal, while colored females experienced a rate only nine times as high. After the first of January, 1919, the excess rate returned slowly to the normal figures. These facts are based on death rate only.

Any comparison of race morbidity or mortality, to be of value, must be based on observations of individuals living in the same climate, in the same domestic environment, and in similar age distribution. It is practically impossible to discover groups living under such conditions. Howard and Love, perhaps, approached more nearly to such an ideal in studying the white and black races in the Army, but even in the military forces many factors are at play. Thus, the death rate among enlisted men was highest among the American troops in the United States (12.02); second in Europe (6.07); third in Panama (1.09); fourth in Hawaii (0.55); fifth in the Philippine Islands (0.14). By race it was highest for the colored troops (12.69); second for the white (8.83); third for the Porto Ricans (7.80); fourth for the Filippinos (2.84); and fifth for the Hawaiians (1.72). The authors point out that while the native troops had higher admission rates than the whites, the death rates were lower, which illustrates the point that the death rate for this type of disease is lower in the summer and in the tropics.