Part 1
INFLUENZA An Epidemiologic Study
BY WARREN T. VAUGHAN, M.D.
BALTIMORE, MD. THE AMERICAN JOURNAL OF HYGIENE Monographic Series No. 1 1921
COPYRIGHT, 1921, BY THE AMERICAN JOURNAL OF HYGIENE BALTIMORE, MD.
PRESS OF THE NEW ERA PRINTING COMPANY, LANCASTER, PA.
PREFACE.
Following every widespread epidemic or pandemic of influenza, the contemporary literature becomes virtually flooded with reports of scientific studies on the etiology and the epidemiology of the disease. By the time that recrudescences have ceased, interest has usually lagged and eventually research in this subject has practically ceased, only to be revived with the development of the next extensive epidemic.
To one who has had occasion to review the extensive literature of the last pandemic, it becomes apparent that many of the recent writers are uninformed, or at best only partially informed, regarding the rather extensive information accumulated during the 1889 epidemic. The longer one studies the observations made in 1889–93 the more firmly convinced one becomes that the recent pandemic was identical with the former in practically all of its manifestations.
It is desirable that, following each epidemic prevalence some individual or individuals review the literature of the preceding epidemics, acquaint himself with what has been written regarding influenza in the intervening time up to the epidemic prevalence and correlate the work done in these two periods with the various reports regarding the latest epidemic.
The following pages constitute an attempt to correlate the epidemiologic observations of the epidemic thirty years ago with those of the 1918–20 epidemic, and with the observations made during the intervening years.
The house census in the City of Boston and the preparation of this monograph were made possible by the financial assistance of the Metropolitan Life Insurance Company. This organization has devoted a considerable sum of money to the study of influenza in its various phases.
The author is indebted to his chief, Dr. Milton J. Rosenau, for helpful advice and criticism and for the inspiration to carry on this investigation. Dr. W. H. Frost has made many valuable suggestions. Appreciation is also due Mr. Edwin M. Knights, who is responsible for all of the charts, and to Mrs. V. K. Davis, who aided in the tabulation of results of the Boston investigation.
The house-to-house census was carried out with the co-operation and assistance of the Federated Jewish Charities in Boston and individual members of the social service departments of the Massachusetts General Hospital and the Peter Bent Brigham Hospital.
THE AUTHOR.
Department of Preventive Medicine and Hygiene, Harvard Medical School, Boston, _September 17, 1920_.
This monograph is one of a series of studies carried out under the supervision of the Influenza Commission of the Metropolitan Life Insurance Company. The Influenza Commission is investigating the etiology and prevention of the acute respiratory diseases, and the work is being carried on in Boston, New York City, Chicago, and Washington. The members of the Commission are Dr. M. J. Rosenau, Chairman, Dr. G. W. McCoy, Dr. L. K. Frankel, Dr. A. S. Knight, Dr. E. O. Jordan, Dr. W. H. Frost and Dr. W. H. Park, Secretary.
INFLUENZA.
AN EPIDEMIOLOGIC STUDY.[1]
BY WARREN T. VAUGHAN, M. D.
(Received for publication April 6th, 1921.)
CONTENTS
SECTION I. 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 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._
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.
The experience of recent years has amply demonstrated that influenza may be characterized by a high mortality or a low mortality; that pneumonia may be prevalent or relatively rare during an epidemic. These features are not truly characteristic of influenza itself. They are phenomena which depend chiefly for their existence on secondary invasion with organisms other than the causative agent of influenza. It may be that the influenza virus itself is capable of producing pneumonia, but it is generally accepted that an overwhelming majority of the complicating pneumonias are due to secondary infections. One perusing the former literature today would hesitate to state that an ancient epidemic was not influenza merely because it was accompanied by high mortality, nor would he wish to say that it was not this disease because there was no mention of a high incidence of pneumonia. We have had both types within the last few years, as in March and April, 1918, when the disease appears to have been accompanied by a very low mortality and a low incidence of pneumonia, and in October of the same year when the pneumonia incidence and the death rate were both relatively much higher.
Attention should be called to a certain inaccuracy which has appeared in the literature and which has resulted in some instances in a misunderstanding of the entire history of influenza. Finkler says: “According to August Hirsch the first influenza epidemic occurred in 1173 and he places it in his work as the first out of eighty.” This has given the impression to some that influenza was unknown previous to that date. Leichtenstern has quoted Hirsch more accurately and thereby given an entirely different meaning to the statement. “August Hirsch says that the first epidemic that can be definitely said to be influenza occurred in 1173.” Jordan also conveys the latter impression. He remarks that the first extensive, well described epidemic of influenza occurred in 1510.
Hirsch places the first authoritative influenza epidemic in the year 1173; Zeviani in 1293; Gluge in 1323; Schweich, Biermer and Ripperger in 1387; while Saillant, Thompson, Zuelzer and Leichtenstern accept nothing prior to the first pandemic of 1510 as being unquestionably influenza. It should be remarked here that opinion is not unanimous in every case as to the identity of all epidemics following 1510.
Hirsch concluded that there have been about eighty epidemics since that of 1173. Parkes states that in the fourteenth century there were six epidemics, in the fifteenth seven, in the sixteenth eleven, in the seventeenth sixteen, in the eighteenth eighteen, while in the first half of the nineteenth ten epidemics are on record.
Table I shows in brief review the occurrence of the more important epidemics since the year 1173. Like all similar summaries given in tabular form it possesses the disadvantage of telling only parts of the entire story, and those in only a very general way, but it will suffice as a resumé and for the emphasis of certain phenomena to which attention will be later directed.
Concerning the epidemic of 1889, it is usually stated that it had its origin in Bokhara in May of that year. As will be seen from the table influenza was present also in Greenland and the Hudson Bay territory in the spring of 1889. The possibility of simultaneous origin in at least two localities in that year will be discussed later. The epidemic remained in Bokhara until August of the same year, after which time it slowly traveled to Siberia where at Tomsk traces of the disease were observed with certainty in October. At that time it was also observed in the Caucasus and in European Russia. It appeared in Petrograd in October, 1889, and remained epidemic until December of that year. The spread of this epidemic throughout the world is indicated in the following table adopted from Leichtenstern:
_Spread of Influenza in 1889–90._
═══════════════════════════════════════════════════════════════════════ Month. 1889–90. ─────────────────────────────────────────────────────────────────────── First (October) St. Petersburg, Moscow, Courland, Livonia, Finland. Second Berlin, Paris, Vienna, Sweden, Denmark. Third London, Holland, Belgium, Balkan States, North America. Fourth Capetown, Egypt, Honolulu, Mexico, Japan, Hong Kong. Fifth San Francisco, Buenos Ayres, India, Sierra Leone, Scilly Islands. Sixth Chili, Kamerun, Zanzibar, Basutoland, Tasmania. Seventh British Bechuanaland, Barbados. Eighth Gold Cost, Natal. Ninth Trinidad. Tenth Iceland, Madagascar, China, Senegal. Eleventh Kashmir, Katunga. ───────────────────────────────────────────────────────────────────────
Between the years 1889 and 1893 according to Leichtenstern there was no period altogether free from influenza. Here and there individual cases or small epidemics sharply localized were observed. In 1893 another epidemic appeared in many places and became quite widespread. There was not, according to this author, the definite geographic progression that had been observed in 1889. This was but a recrudescence, a lighting up from endemic foci remaining after the first wide spread. In the first half of 1893 there was a light spring epidemic, and in November of the same year a larger epidemic swept over the whole of Europe. The height of the latter was reached chiefly in December.
The influenza incidence subsequent to 1893 will be discussed later.