Among all infectious diseases there is none which affects the entire population, irrespective of age and condition, in so short a time as pandemic influenza.
An enormous morbidity with a relatively very small mortality is one of the preeminent characteristics in the epidemiology of pandemic influenza, and a sign of great assistance in judging doubtful epidemics of preceding ages. Remarks like "vix unus evasit," "nemini pepercit," "correpti sunt fere omnes," occur everywhere in the writing of the older authors, together with the remark that except the aged, the weakly, and the phthisical, no one died of the disease.
The mass of figures that has been accumulated in collective investigations and official reports as regards the question of morbidity rests largely upon estimated numbers by medical observers. No wonder, then, that the figures vary considerably, even from the same districts.* There is, however, no doubt that considerable differences in the percentage incidence existed in different localities. The majority of the 3304 reporters to the German collective investigations agreed upon a morbidity of from 40 to 50 per cent, of the population in their respective districts.
Similar averages were arrived at in St. Petersburg, Paris, and Budapest (50 per cent.), Vienna (30 to 40 per cent.), Massachusetts (collective investigation, 39 per cent.), and Antwerp (33 per cent.). In France the influenza morbidity was calculated by the statistician Bloch to be 75 per cent, of the entire population. The figures (in nearly all cases above 50 per cent.) of the Swiss report for the various cities and districts of that country are very high. In contrast to this are the figures from Munich, calculated on the medical notifications, not very reliable for this purpose-22 per cent.; and London, 34 per cent. Parsons tells us that the morbidity in London in the epidemic of 1782 amounted to three quarters of the population; in 1837 to one half, and in 1847 to one quarter, of the entire population, and that in the epidemic of 1889-1890 it certainly did not amount to more than one quarter of the entire population.
The period of estimates was followed by a period of statistics, and now a considerable difference was revealed. The influenza morbidity of the various workmen's clubs, of the officials and servants of the postal and railway systems, and in England too among the large banks and business houses, was almost always considerably less than that estimated by the medical attendants. The following extract from the statistics will show this:
The morbidity amounted to-
Ortskrankenkasse, Berlin (258,090 members)............... 1.7 per cent.
Betriebskrankenkasse, Berlin (24,454 members)............ 3.2 " "
Ortskrankenkasse, Strassburg (5692 persons).............. 6.2 " "
Eisenbahnkrankenkasse, Strassburg (903 persons)..........14.7 " "
Factory population, Alsace-Lorraine (18,620 persons).......24.7 " "
Employees of Bavarian state railroads (12,718 persons)......22.0 " "
Day laborers on Bavarian railroads (14,213 persons).......23.0 " "
Chief Postal District of Dresden (2927 persons;.............17.4
Number of factories in Baden (3140 persons)..............30.0 " "
Rural District Segeberg,** Schleswig (18,216 persons)......33.0 " g*
District, Triberg *** (11,054 persons).......................35.0
Collective investigation in Strassburg § (2379 persons).......36.5
Factory workers of the Parish of Triberg (1791 persons).....44.2 " "
General post office in London (6872 persons)...............33.6
Bank of England (1117 persons) .........................20.8
London and Westminster Bank (502 persons)..............21.0 "
Great Eastern Railway (15,261 persons) ....................13.8
London and Northwestern railway (59,731 persons)....... . . 6.4 " "
German army (including navy) ..........................10.0
* Compare Rahts, "Deutsche Sammelforschung," p. 48, P. Friedrich, loc. cit., p. 181, ff.
**Local collective report. *** House to house count.
§ Collection of a number of seminaries and factories, including police and street railway employees.
The remarkably slight mortality just quoted in several of the sick clubs, etc., is unquestionably due to the fact that many persons who were only slightly affected continued their work or only remained idle for a very few days, and were thus excluded from the statistics. Similar circumstances probably explain the strikingly small statistical morbidity of the German army.
A very different picture is shown by the schools, seminaries, pensions, orphan asylums, workhouses, etc. A glance at the comprehensive statistics of P. Friedrich,* Parsons, Schmid, and others shows us that these institutions had an enormously high morbidity-usually 60 per cent, and over. The statistics of all countries show the same (Combe,** Comby ***).
The general impression which one receives after looking into the interminable morbidity statistics is that the estimates made by the German doctors quoted above were not too high. If, in addition, we remember that many slight cases did not come under the observation of any medical attendant and were not included in the statistics, we shall not err greatly in concluding that the epidemic of 1889-1890 affected about one half of the inhabitants of Germany.
That the general morbidity in the later epidemics did not approach that of the pandemic every one has had the opportunity of observing. The same thing is proved by the numerous statistics of Germany and England (Wutzdorff, Parsons).
In these after epidemics also the schools, orphan asylums, pensions, workhouses, etc., still show a decidedly greater morbidity than the general population.
As regards the so called miasmatic explanation of the suddenness of the general infection, we must refer to what we have previously said (p. 544). Even if the epidemic of 1889 did not begin in the explosive manner generally accepted, so that "every one was affected at the same time," even if, as was proved, isolated cases everywhere preceded the epidemic outbreak, yet there is no doubt that a rapid development of the epidemic often did occur in the form of a sudden infection of the population. §
Examples of this occurrence are found in great number in the history of influenza and also in the last pandemic. We would refer to our remarks above in reference to the frigates "Stag," "Canopus," and "Saga" (see p. 559); also to the epidemic of the Grands magasins du Louvre,