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.