Occurrence Since 1893.
Attempts even today to determine when and where influenza has prevailed in the world since the great pandemic of the last century are met with great difficulties. There are several reasons for this, chief among which is the absence of definite characteristics by which the disease may be recognized. The isolated solitary case baffles positive diagnosis. Nearly every year there are reports in the literature of small outbreaks in institutions or communities in which the clinical picture is that of epidemic influenza. As a rule the conclusion has been in these cases that because the bacteriologic findings did not show a predominance of Pfeiffer’s bacillus the epidemic was not true influenza. This is particularly true in the outbreaks in which the streptococcus predominated. Today our views concerning the bacteriology have changed distinctly, and I believe it is safe to say that the predominance of a streptococcus in a local epidemic in no way rules out influenza, and that the only criteria by which we may judge are the clinical picture and the evidence of high infectivity, together with the epidemiologic characteristics of the local outbreak.
Period 1893–1918.—A review of the medical literature between 1889 and 1918 gives one a certain impression which may be summarized as follows: Between 1890 and 1900 the disease was in general more highly prevalent in most localities than at any time during the preceding thirty years. At no time during this decade did the annual death rate from influenza in England and Wales fall to anywhere near the figures that had prevailed consistently between 1860 and 1889. Between 1900 and 1915 there was a gradual diminution, but still not to the extent that had prevailed previous to 1889. Since 1915 there appears to have been a gradual increase. During the entire period there has been difficulty in distinguishing between the disease in question and other respiratory tract infections, particularly coryza, sore throat, tonsillitis, and bronchitis. Many of the local epidemics which appear probably to have been true influenza have had associated with them a high incidence of sore throats. We describe this as sore throat, rather than tonsillitis, because the clinician remarks that although the throat is sore there is little if any demonstrable inflammation of the tonsils.
Chart VIII published by Sir Arthur Newsholme, showing the death rate per million of population from influenza in England and Wales gives some idea of the prevalence of the disease in the first part of the interpandemic period in those countries. It should be remarked that the record is for deaths from influenza only.
For records in this country it is convenient to refer to the death rate in the State of Massachusetts; first, because the records in that State have been carefully kept for a long period; and second, because influenza has been carefully studied in this State during both epidemics by two most competent epidemiologists. For the period preceding 1889 we quote herewith from Abbott:
“For the past 45 years or more, or during the period of registration which began with the year 1842, no epidemic of influenza has prevailed within the State to such an extent as to have manifested itself in any serious manner in the annual lists of deaths. An examination of the registration reports for each year since 1842 shows that in no year were recorded more than 100 deaths from this cause; the highest number from influenza in a single year (92) occurred in 1857, and the least number (8) in 1884. The average annual number of deaths from this cause reported in the State for the period 1842 to 1888 was 38. The average number during the first half of this period was greater than that of the last half, especially when considered with reference to the increase of population. From these statistics of nonepidemic influenza between the years 1842 and 1888 it appears that its greatest prevalence, or rather the years in which the mortality from this cause was greatest, were also years of unusual mortality from pneumonia, and in some instances from bronchitis.”
Frost has charted the death rate per 100,000 from influenza and from all forms of pneumonia in Massachusetts by month, from 1887 to 1916. From it he concludes that the epidemic of 1889–1892 developed in three distinct phases, the first culminating in January, 1890, the second in April and May, 1891, and the third in January, 1892. The mortality was higher in 1891 than in 1890, and still higher in 1892, while in 1893, although there was no distinct epidemic, the pneumonia mortality for the year was even higher than that of 1892. Frost remarks that this corresponds to the experience in England, and that it apparently represents the general experience in other countries (see charts IX and X).
CHART VIII.
Death rates per million from influenza in England and Wales from 1845 to 1917. (Newsholme.)