Influenza

SECTION I.. Page

PAGE

GENERAL EPIDEMIOLOGIC CONSIDERATIONS 1

Historical 2

Clinical and epidemiologic identification 13

General characteristics of early epidemic outbreaks 14

Symptoms in former epidemics 19

Manner of spread 20

Human intercourse 23

Crowd gatherings 26

Mass attack 27

Healthy carriers and convalescents 30

General manner of spread in individual localities 31

Primary type of epidemic 31

Secondary type of epidemic 33

Mortality curves 36

Duration of explosive outbreak 37

Morbidity curves in 1920 recurrences 41

Spread in countries and continents 42

Spread in primary waves 42

Spread in recurrences 44

SECTION II.

INFLUENZA EPIDEMICS SINCE 1893 47

Occurrence since 1893 47

Period from 1893–1918 47

Increase in 1900–1901 49

Period from 1901–1915 51

Influenza in 1915–1916 55

Influenza between 1916 and 1918 58

The pandemic of 1918 59

Date of first increased prevalence in various localities 65

Influenza in China 80

Autumn spread in the United States 81

Recrudescences 87

Recurrences in the winter of 1919–1920 89

The winter of 1920 90

Incubation period 95

Predisposing causes 96

Periodicity 97

Virulence enhancement 108

Meteorologic conditions 113

Secondary invaders 114

Origin of the 1918 pandemic 116

SECTION III.

AN INVESTIGATION OF INFLUENZA IN BOSTON (WINTER OF 1920.) 127

Diagnostic standards for the 1918 epidemic 134

Standards for 1920 134

Morbidity 137

Relation of sex to morbidity 143

Relation of sex to severity 145

Morbidity by age 145

Relationship of occupation to morbidity 150

Effect of race stock 155

Mortality 156

Mortality by sex 165

Relationship to age 167

Relationship of occupation 170

Density of population 170

Race stock and mortality 173

SECTION IV.. An Intensive Study of the Spread of Influenza in Small Groups of

AN INTENSIVE STUDY OF THE SPREAD OF INFLUENZA IN SMALL GROUPS OF CLOSELY ASSOCIATED INDIVIDUALS 175

Effect of overcrowding 179

Domestic cleanliness 187

Economic status 189

Distribution of the disease through the household 191

The first case in the family 194

Intimacy of family contact 197

Recurrent cases 198

SECTION V.

IMMUNITY 199

SECTION VI. INFLUENZA AND OTHER DISEASES 212

Influenza and tuberculosis 212

Other infectious diseases 220

Encephalitis lethargica 222

SECTION VII. COMPARISON OF INFLUENZA WITH OTHER EPIDEMIC DISEASES 224

Epizootics 224

Asiatic cholera 228

Epidemic meningitis 228

Plague 229

Measles 231

SECTION VIII.

THE PREVENTION AND CONTROL OF INFLUENZA 234

Anticipatory or preventive measures 236

Organization of health services 237

Palliative measures in the presence of an epidemic 239

Problems for the future. Constructive research 241

Bibliography 245

Footnote 1:

From the Department of Preventive Medicine and Hygiene, Harvard Medical School, Boston, Mass.

INFLUENZA.

AN EPIDEMIOLOGIC STUDY.

SECTION I.. _general Epidemiologic Considerations._

General Epidemiologic Considerations.

Those who seek to find in a study of the epidemiology of epidemic influenza the secret of the causation of the disease, and its ultimate eradication, are probably predestined to at least partial failure. We must call upon the bacteriologist for information as to the causative organism, and in time he may be able to furnish us with satisfactory prophylactic measures, particularly with a successful vaccine.

But while pure epidemiologic studies will not demonstrate the ultimate factor in the etiology, nevertheless these studies do subserve several most important functions. The bacteriologist, the immunologist, the serologist have accumulated a wealth of information since the 1918 pandemic, but as far as definite conclusions concerning the causative agent of the disease are concerned we are no nearer to the truth than we were at the time when Pfeiffer made his original observations. There is no incontrovertible evidence by which one may say that the influenza bacillus is or is not the cause of the disease. We must therefore await further studies and future discoveries. But we cannot await idly in the knowledge that new epidemics of the dread disease will surely come, probably mild ones in the next few years, and certainly severe ones again within a few decades. We must amass all of the available information concerning the mode of action of the disease, its manner of spread, its degree of infectivity, its distribution and the mode of its recurrences, and try to formulate from a study of the available facts some means of protecting ourselves against the epidemic, if not of preventing it entirely.

In short, in the present state of the bacteriologic knowledge of the disease, we may say that the epidemiologic features are the only facts upon which we have to build in planning our defense. Today, the practical work in the eradication of influenza must depend chiefly, if not solely, on the general methods of preventive medicine.

Many valuable monographs have been written on the subject, particularly following the pandemic of 1889–1893, but these have all emphasized features and phases of the disease which seemed at that time to be particularly important. Facts which seemed of extreme importance to the earlier writers are today in some instances considered relatively unimportant, while other phenomena which were but touched upon by the former investigators today have assumed deep significance. For this reason it is worth while to reproduce here the observations made in previous epidemics, and to correlate them with the facts developed in the abundant literature of the last few years, and to draw therefrom inferences as to the life and habits of the influenza virus, and conclusions as to the means of interrupting its progress.

HISTORICAL.

The history of influenza can justly be divided into two phases, the first ancient, and the second modern. The latter period begins with the 1889 pandemic. By that time the science of bacteriology had altered our concepts of the etiology of disease and epidemiologists had begun to avail themselves of statistical methods of analysis. For the purposes of this paper, therefore, consideration will be given chiefly to the epidemic of 1889, and a summary of earlier epidemics will be made merely to refresh our minds concerning the antiquity of the disease and the periods of its occurrence. References to the earlier epidemics will be made more particularly in the special discussions later, where points of similarity or difference will be brought out. Further than that it is unnecessary to go in the history of the disease, for the several excellent monographs of 1890 to 1900 tell the historical story in a manner that could scarcely be improved upon.

The great antiquity of epidemic influenza is a fact which I think may be admitted in spite of some who hesitate to accept it because of lack of convincing descriptive evidence. Some believe that the epidemic of the year 412 B.C., described by Hippocrates and by Livy, was an epidemic of influenza. Some have suggested that the epidemic described by Thucydides was the same disease. Parkes remarks that the epidemic pervading the Athenian Army in Sicily in 415 B.C., recorded by Diodorus Siculus, has been supposed to have been influenza. Finkler, in referring to a report by Diodorus of a pestilence occurring in 395 B.C., which broke out in the Greek Army at the siege of Syracuse, and which killed off the soldiers murderously, says that this could not have been influenza. He regards as sufficient argument the fact that the mortality was high. After the epidemic of 1918, one is more inclined to believe that the epidemic in Sicily may well have been true influenza. We must remember that previous to the last few pandemics the stories have been fragmentary in character and were told, not by physicians, but chiefly by the historians of the time, men who have desired to impress their readers with some idea of the horrible ravages of the disease, and who have doubtless in some instances transmitted the impression of monstrous mortality rates. The early historians were much given to figures of speech, many of which were very telling in conveying the impression desired. Finally, the writers of the middle ages and of earlier times had little or no statistical material on which to base their conclusions. I have no doubt that a historian who during the 1918 epidemic of influenza might have limited his observations entirely to the disease as it occurred at Camp Sherman, Ohio, and who saw 125 robust soldiers dying each day, would have truly written that the disease killed off the soldiers murderously. A further statistical argument in favor of considering the epidemic among the Greek soldiers as quite possibly influenza is the fact that as shown by present day findings these men were all of the age in which the mortality is highest, and were living under sanitary conditions which predispose to high incidence and high mortality.

According to Parkes, in 827 A.D., an attack of “cough” which spread like the plague was recorded. In 876, Italy and later the whole of Europe was attacked, and the army of Charlemagne, returning from Italy, suffered greatly. “Dogs and birds were attacked at this time.” In 976 the whole of France and Germany was attacked by a fever whose principal symptom was cough. There is also record of diseases which may have been influenza which were seen in Germany and France in 927 and in England in 996 and 997. All of these records are indefinite and from their nature unconvincing to a critical student. Several investigators have gone over these past records up to 1889 with the idea of determining definitely what plagues were, and which were not, true influenza. The criteria used by the various investigators have differed slightly in some instances. For instance, one chooses to use the record of low mortality in widespread epidemics as the chief characteristic of pandemic influenza, while another emphasizes principally the complications.

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