Although there can be no doubt of the relationship of the previously mentioned world pestilences to true influenza, as regards the other outbreaks, to which we have also alluded, the numerous so called "influenza epidemics," there is considerable doubt.
The designation "la grippe," or "influenza," has been current over all the world for a very long time, and is even applied to "a febrile catarrh" of the respiratory tract which occasionally shows a slight epidemic character. It is common practice to designate as grip a comparatively severe "cold," with implication of the tracheobronchial mucous membrane, particularly if the clinical course is characterized by fever and great prostration, and if the disease affects several members of a household or several families in a locality.
There can hardly be a doubt that the schematic chronology compiled by historians of influenza epidemics is often unreliable. This is due to the almost unavoidable (because of the absence of sufficient data) inclusion of numerous epidemics of "catarrhal fever" and "cold." In this respect J. Seitz was perhaps the greatest offender; in his well known monograph, "Catarrh and Influenza," he regarded both diseases as identical and worked them up into a common statistical mass.
We cannot go into a critical analysis of the earlier influenza epidemics ; but a brief review of the pandemics which immediately preceded the latest one will make sufficiently evident the difficulties mentioned above.
It is by no means certain that the limited local epidemics recorded by Korman in 1870 in Coburg, and by 0. Seifert in Wiirzburg in 1883, were identical with what nowadays we call influenza. In the epidemic recorded by Kasin in Russia from 1856-58 the frequent occurrence of certain complications, such as swelling and abscess formation of the glands of the neck, especially of the parotid, purpura, and scurvy, raises suspicions as to the nature of the disease.
W. Ziilzer, in 1886, stated: "Even up to the most recent times, influenza keeps up its great marches; at the time at which I am_writing these lines, we in Berlin are in the midst of an epidemic of considerable magnitude, where the sick may be counted by the thousands "; the question naturally arises, Was this the same influenza which, three years later, attacked the entire world, and, when it reached Berlin, appeared to the selfsame physicians as an entirely new disease?
The evidence of the epidemic recorded by R. van den Velden in Strass burg in 1874-75 is decidedly more convincing, not only on account of the frequency with which pneumonia was noted as a complication, but chiefly because simultaneously an epidemic was noted in several districts of France, southern Germany, and the Rhine provinces.
It is very questionable whether the epidemics recorded in 1855 and 1862 in Iceland; 1870 in Philadelphia; 1875 in Scotland by Gairdner; 1870 by Handheld-Jones; 1876 in the Fiji Islands; 1887 in various districts of England; in October, 1889, in Natal; in November in Jamaica and Prince Edward's Island-can be classed as true influenza, even when the frequency of pneumonia, especially in the last two districts mentioned, is taken into consideration. As regards the influenza epidemic which in November and December of 1889 existed among the school children of Pleshey and Great Waltham, and which affected at least 50 per cent., apart from the fact that the pandemic did not appear there until January 1890, the circumstance that the school children exclusively were affected, is in itself suspicious. Grave doubts must also be entertained in respect of the universally quoted and celebrated "spring catarrh epidemic," which is generally regarded as influenza, which occurred in St. Kilda, Faroe, and Nikobar Islands, etc.
The collective investigations of the last pandemic contained a number of reports based upon retrospective diagnosis, alleging that in numerous districts in Germany "first cases" were observed and even small epidemics took place in the summer and fall of 1889, several months before the actual outbreak of the pandemic in December.
As the result of my own experience regarding the identity of those outbreaks which arose before 1889 and of the small outbreaks of "catarrhal fever and cough epidemics" which have usually been classed as la grippe or influenza, with the true influenza which we learned to appreciate for the first time in the winter of 1889-90, I am of opinion that they were not the same disease. This last real influenza gave the impression of being an affection entirely different from those diseases which up to that time had been generally designated as la grippe, not alone by its appearance as a pandemic world pestilence and the sudden development of the disease in the majority of the population, but also by its character as a severe general infectious disease, by its entire clinical course, its various and often dangerous complications and sequelae.
If the micro organism discovered by R. Pfeiffer maintains its place as the exclusive cause of true influenza, the diagnosis and history of influenza epidemics will have made a decided advance toward certainty of identification in the future. Even if it be too much to expect every practising physician to make his diagnosis depend upon the finding of the bacillus of influenza, the occurrence of an epidemic will give rise to a number of cases in which the specific bacteria will be isolated, so that any existing epidemic may be recognized with certainty as true influenza.
Should, however, the numerous influenza outbreaks and epidemics which A. Hirsch has tabulated in his historic and exhaustive work prove to be one and the same species of influenza,-a possibility that cannot be simply neglected,-influenza would show itself, in respect to its epidemiologic features, as an exceedingly variable and protean affection. It would be possible, under the conditions mentioned, to give the following epidemiologic definition of influenza:
Influenza is a specific infectious disease and usually arises epidemically, but it is, in fact, endemic over all the world (sporadic cases), although in any particular district or place years and decads may pass before the disease shows any great epidemic development. An epidemic of the disease is demonstrable nearly every year in some part of the world. There occurs then, from time to time, starting in some part or center, or from several places simultaneously, from unknown causes, an enormous increase in virulence of the specific micro organism, with accompanying increase of contagiousness. These are the periods in which influenza spreads in the form of a mighty epidemic over entire countries, a hemisphere, or the entire earth. Our common endemic "influenza " or "grip," which generally occurs sporadically or as a mild epidemic, belongs to the same species of disease as the world pestilence, influenza. It is, however, less virulent and the specific cause has less vitality.
For the present, until a final decision is arrived at by means of bacteriology, we maintain that influenza nostras and pandemic influenza are just as distinct diseases as are cholera nostras and Asiatic cholera. According to this view, we divide the diseases designated as influenza as follows:
1. Into the pandemic influenza vera, due to the bacillus of R. Pfeiffer.
2. The endemic epidemic influenza vera, which develops after a pandemic from the residual germs (bacillus of R. Pfeiffer). The duration of this endemic stage of influenza vera may last several years in individual districts.
3. The endemic influenza nostras s. notha, pseudo influenza, catarrhal fever, vulgo grippe, a disease sui generis. The microorganisms of this disease are as little known at present as are those of cholera nostras.