Part 20

Per cent. The year 1917 11.2 6 winter months, 1917–18 23.1 5 summer months, 1918 18.8 4 autumn months, 1918 (Influenza period) 34.4

“It is not strange that once pneumonia has secured a foothold in patients already weakened by influenza their chances of recovery were lessened.”

Woolley reports that for the troops stationed at Camp Devens, Mass. there were no fatalities from uncomplicated influenza. In every fatal case but two a diagnosis of pneumonia was made, and in these two cases pure cultures of pneumococcus were obtained from the blood after death, so it appears that they were cases of pneumococcus septicemia. Up to October 29, 1918, 19 per cent. of the total number of influenza cases reported developed pneumonia and of these there was a case mortality of 27.9 per cent. The mortality rate among the influenza cases was 5.4 per cent.

At Camp Humphreys, Virginia, 16 per cent. of the camp was attacked by the disease; 28 per cent. of influenza cases had pneumonia; 10 per cent. of influenza cases died; and 35 per cent. of pneumonia cases died. One and six tenths per cent. of the population of the camp died from influenza. The camp had an average strength of 26,600 individuals. Fifty-two per cent. of the entire number of cases occurred during the peak week which ended October 4th.

Between September 21st and October 18th, 1918, 9,037 patients were admitted to the Base Hospital at Camp Grant. This represented about one-fourth of the strength of the camp. Of these 26 per cent. developed pneumonia and 43 per cent. of the pneumonia cases died. Death occurred to about 11 per cent. of the total admissions.

The death rate at Camps Devens, Sherman and Grant were among the highest of all of the camps in this country. The annual death rate from all causes per 1,000 for the four last months of 1918 were 132 for Camp Cody, 123 for Syracuse, 116 for Camp Sherman, 102 for Camp Beauregard, 97.3 for Camp Grant, 75.0 for Camp Dix, 67.0 for Camp Devens. These seven camps stood out high above the majority. By far the majority, 28 camps, had an annual rate between 61.9 and 25.5 per 1,000. Only four camps recorded lower rates than the latter figure.

The Municipal Statistics of Paris showed that during the first half of October, 1918, the average weekly mortality was from two to three times that of nonepidemic years. The returns for the Departments of France also showed a mortality three times above the average for previous years, though not uniformly so. In the Departments the mortality from influenza did not exceed 10 per cent. and in many cases it was below 5 per cent. On the other hand cases admitted to hospital, which consisted of the worst forms of the disease, showed a mortality varying between 12 and 30 per cent. Returns received from Italy were similar. The disease in that country was especially severe in the northern part and in the provinces bordering on Switzerland. Marcus, of Stockholm, reported in September, 1918, that the epidemic in Sweden was running a very severe course, more than 1,000 deaths having occurred up to the time of his report. According to Weber, 2,770 deaths occurred in Berlin during October, 1918, from influenza and pneumonia alone. In Vienna there died from influenza between September 1st and October 19th, 1918, 3,125 persons. The deaths in Vienna from influenza and pneumonia normally total 40 to 50 per week. At the highest point of the epidemic this number had increased to 1,468. Böhm estimates the total influenza incidence in Vienna as 180,000 cases, with a probable mortality around 1.7 per cent. Dunlop estimates that the total number of influenza deaths in Scotland in the winter of 1918–19 may be assessed at 20,000.

A. Giltay has compared the epidemics of 1890 and 1900 with that of 1918 as regards mortality, in Amsterdam. He has studied figures for seven consecutive weeks in each of the three periods under observation and found that the maximum figures for mortality were 61.5 in 1890, 41.2 in 1900, and 52.7 in 1918, but if these figures are compared with the average mortality for the year it is found that the increase of mortality as the result of influenza alone is 39.3 for 1890, 24.5 for 1900, and 40.3 for 1918. Thus the present epidemic is more severe than that of 1890.

Many reported mortality figures are without value because they are either death rates in selected groups such as those in a hospital, or, because the report does not state the status of the individual. Thus, Hoppe-Seyler stated at a meeting of the Kiel Medical Society that of 577 cases treated in the Municipal Hospital, nearly all of which were severe, 28.9 per cent. died. This was reduced to 18 per cent. after deducting the cases admitted in a moribund condition. Again, Rondopoulos reports that the October wave in Greece resulted in a mortality of from 15 to 24 per cent, in different localities.

Just as current vital statistics are of little value in determining the morbidity rate, so also they cannot be relied upon in obtaining fatality percentages. In organizations such as the Army, where all cases are reported, we may get some idea of the fatality rate. The deaths in the United States Army have already been discussed. Marcus, of Stockholm, reports that the military records showed that there had been 34,000 cases in the Swedish Army, with 444 deaths, making a mortality of 1.3 per cent, in that Army.

House surveys also give a fair idea of the mortality. Winslow and Rogers conclude that the fatality rate was as a rule somewhere between two and four deaths per 100 cases, the lower being more likely to be correct. Reeks found in his house census that there had been 3.9 deaths per 100 cases in the autumn of 1918. Carnwath reports that Dr. Niven, in his census, discovered that out of 1,108 cases in the spring and autumn of 1918 there were but 15 deaths, which would give a fatality rate of 1.3 per 100 cases.

Frost has found from his large survey that the ratio of deaths to total cases of influenza varied in the localities surveyed from 3.1 per cent. in New London as a high point to 2.8 per cent. in San Antonio, Texas. There was some apparent relationship between fatality rate and geographic distribution, the higher rates being in San Francisco on the Pacific Coast, and in the localities studied on the north half of the Atlantic Seaboard, and the lower rates being in the central and southern states. The fatality rate on the Pacific Coast was 2.33, on the Atlantic Seaboard 2.05, and in the last district 1.08 per cent.

Our own figures correspond very closely with those of Frost. Among the 10,000 living individuals surveyed in 1920 there were 1,970 cases of influenza in 1918. Add to this the 50 deaths for 1918, which were not included in the 10,000 living individuals, which makes a total incidence of 2,021. This case fatality rate of 2.47 per 100, corresponds closely to Frost’s rate for the North Atlantic Seaboard.

The relative mildness of the 1920 recurrence is indicated in the lower case fatality rate. Fourteen out of 955 cases died, giving a rate of 1.47 per 100 cases.

_Mortality by sex._—There is not a uniformity of opinion as to which sex suffered the higher fatality rate during the 1918–19 spread. Winslow and Rogers found for Connecticut a distinctly heavier mortality among males for the last four months of 1918, 58 per cent. of the influenza-pneumonia deaths being among this sex. They believe that this is probably due to a greater exposure to the original infection.

Fränkel and Dublin point out that in a study of 70,729 policy holders of the Industrial Department of the Metropolitan Life Insurance Company in the period from October 1, 1918, to June, 1919, the death rates for males and females were practically the same for both white and colored individuals.

The excess of males over females among the whites is only three per cent., and there was no excess among colored. In contrast, the respiratory diseases, including influenza-pneumonia, under normal conditions, show a higher mortality incidence among males than among females. In the seven year period from 1911 to 1917 the mortality rate showed an excess of 18 per cent. males over females, among whites, and of 30 per cent. among colored. This would seem to indicate that the effect of the epidemic was not much, if any, greater on males than on females, and suggests that the excess mortality caused by the epidemic did not operate on the sexes as the normal mortality from influenza-pneumonia had in previous years.

Dunlop finds that in a study of 10,797 deaths registered in Scotland up until the end of December, 1918, 52.44 per cent. were females and 47.56 were males. These were for deaths reported as due only to influenza. Apert and Flipo found a decided predominance among the female deaths in Paris. In both of these observations the absence from the civilian population of male inhabitants of military age obscured correct comparative statistics.

Once again, Frost gives the most comprehensive discussion of the subject. He found, as we have stated, that the influenza case incidence in persons over fifteen years of age was higher in females than in males, and that in persons under fifteen the relative incidence as between males and females is variable, but with very slight excess in males for the localities studied, combined. On the other hand, the case fatality, the per cent. of influenza cases dying, under fifteen years of age, was higher in females than in males. Over sixty years of age it was considerably higher among the females, but between the ages of fifteen and sixty the general tendency was to a much higher case fatality among the males. The difference was greatest between the ages of 20 and 40. The case fatality between the ages of 15 and 45 in the group of southern and central states was in decided contrast to that in the Northern Atlantic and Pacific groups, the case fatality in the former being remarkably low in both sections and slightly higher in females than in males. He suggests that in the south and middle west where the epidemic was generally milder in respect to mortality than in the northeast and far west, the essential difference was not in case incidence, but in case fatality, especially in persons from 15 to 45 years of age, and in the relatively low case fatality among young male adults. Frost makes the important point that the relative mortality is determined more accurately by case fatality than by case incidence, and that without a full and exact knowledge of the variations in case fatality, statistics of mortality are by no means translatable to terms of relative morbidity. The fact that certain cities showed, as described by Pearl, relatively high mortality rates, does not give conclusive evidence that the morbidity was higher in these cities than elsewhere. The lower influenza case fatality in females from 15 to 60 years of age appears to be accounted for in part at least: first, by a decreased incidence of pneumonia as compared with the males; and, second, by a lower fatality in those cases which did develop pneumonia.

The relatively small number of fatalities in our own records do not warrant a classification by age groups. We found that for all ages in 1918 7.9 per cent. of females developed pneumonia as contrasted with 6.8 per cent. males. This does not include those who died. In 1920, 1.87 per cent. of the male cases died, while only 0.37 per cent. of the females died. Five and fifteen-hundredths per cent. of all male cases developed pneumonia and recovered, and 3.56 of the females did likewise. In 1920 a higher proportion of males than females developed pneumonia, and likewise a higher proportion died.

_Relationship of age._—Leichtenstern has summarized the results for the epidemic of thirty years ago, in saying that the death rate for children under one year was little disturbed by the influenza epidemic; that there was very little increase in mortality in the other ages of childhood; that the higher age periods showed the greatest relative mortality for the disease. On the contrary, the records for England and for Switzerland showed during those periods a higher death rate in children up to five years of age.

Percentages. Ages. 1847–8 1890 1–5 10.5 5.2 5–20 13.1 4.3 20–40 3.8 4.7 40–60 18.5 36.2 60–80 16.9 22.4 Above 80 8.6 2.5

Giltay has compared the age mortality in Amsterdam in 1890, 1900 and 1918 as shown in the following table:

═══════╤═══════╤═══════╤═══════╤═══════╤═══════╤═══════╤═══════╤═══════ │ Under │ │ │ │ │ │ │ │ one │ 1–4 │ 5–13 │ 14–19 │ 20–49 │ 50–64 │Over 64│Total. │ year. │ │ │ │ │ │ │ ───────┼───────┼───────┼───────┼───────┼───────┼───────┼───────┼─────── 1890│ 8.4│ 8.1│ 2.3│ 3.0│ 30.7│ 19.3│ 28.1│ 100 1900│ 9.7│ 8.8│ 1.6│ 3.2│ 17.6│ 18.3│ 40.8│ 100 1918│ 3.0│ 13.0│ 8.7│ 8.3│ 51.9│ 8.7│ 6.4│ 100 ───────┴───────┴───────┴───────┴───────┴───────┴───────┴───────┴───────

Evans has studied the records for the city of Chicago in the epidemic of the year 1890, and found that the number of deaths was highest among persons from 20 to 40 years of age. The greater increase above the expected was in deaths of persons over 60 years of age. Children of school age seemed to enjoy some relative immunity, as shown in the mortality reports.

This latter age grouping for 30 years ago corresponds with those of 1918. Frost found that the death rate per 1,000 was notably high in children under one year of age, in adults from 20 to 40, and in persons over 60. The case fatality from pneumonia in his series tended to be fairly constant, around 30 per cent., except in San Antonio, Texas, where it was only 18.5 per cent. Case fatality was also higher in the following age groups: Under one year, 20 to 40, and over sixty.

This age distribution was probably the same in all countries. Filtzos, describing the epidemic in Greece, said that the ages that suffered most and had the most fatal cases were between 20 and 45. In Spain in May and June of 1918 the mortality was much lower among children and the aged than it was among the adults, especially between 20 and 39 years of age. The disease appeared fatal almost exclusively in these ages. In Vienna, 29.5 per cent. of all the fatal cases were between the ages of 20 and 30. Hoppe-Seyler stated that the ages of most of the cases were between 20 and 40 and the majority between 30 and 40, but that the mortality was highest among the older patients.

Dunlop found that in Scotland the most frequent ages at death were between 25 and 35, 25.28 per cent. of the total being between these two ages. 53.85 per cent. of the total deaths were between 15 and 45 years. The highest age group death rates occurred in age groups 75 and over, and 25 to 35, the former being 7.87 per 1,000, and the latter 7.12. High rates also occurred in age groups under one, and 65 to 75, the former being 6.49, and the latter 5.33. The lowest age group death rates were found in the groups which included children of school age, 5 to 15, being 2.20 per cent., and the age group 10 to 15, being 1.80 per cent. Dunlop has apparently only included those cases in which influenza was diagnosed as the cause of death, and has omitted all in which the diagnosis was bronchitis or pneumonia.

The Bureau of the Census has issued a report based on the mortality in Indiana, Kansas and Philadelphia, for the period September 1st to December 31st, 1918. It shows that the highest rate occurred in the age period from 30 to 34 years, with the period from 25 to 29 second. Of all the deaths tabulated more than half occurred between the period of 20 to 40, although this age group represents only 33 per cent. of the total population concerned.

Age mortality has been studied thoroughly by Winslow and Rogers in Connecticut:

“The four last months of 1917 show a normal age distribution with one quarter of all deaths occurring under five years of age, one quarter between 5 and 40 years, and one-half over 40 years, the proportion of the infant deaths decreasing and the proportion of deaths in old age increasing as one passes from the season of intestinal disturbances to the season of respiratory diseases. In 1918 the distribution of deaths from all causes is strikingly different. Instead of less than a quarter of all deaths occurring between the ages of 5 and 40 years, this period included 49 per cent. of all deaths in 1918; and the two decades between 20 and 40 included 40 per cent. of all deaths (as against only 14 per cent. in 1917).

“Considering influenza and pneumonia alone, these two decades included 56 per cent. of the deaths, while only nine per cent. occurred at ages over 49. The decade between 20 and 29 was most severely affected, including 30 per cent. of all deaths, while the decade between 30 and 39 was a close second with 26 per cent. An even higher incidence occurred at ages under five years, as has been brought out in other investigations, since this age period contributed 16 per cent. of all the influenza-pneumonia deaths. The proportion of deaths from all causes in infancy did not rise even to normal, but with the enormous rise in total deaths the maintenance of a nearly normal ratio, of course, means a heavy influenza mortality.”

Jordan observes in his analysis a low pneumonia incidence among the pupils of elementary and high schools. There were no deaths in 188 cases.

Wollstein and Goldbloom report that in a series of 36 children with influenza and bronchopneumonia at the Babies Hospital in the City of New York, 66.6 per cent. died. Achard and his co-workers review a similar series of 32 infants in Paris with influenza. Eight of the 32 died. In both of these studies we are dealing with selected groups of hospital cases and the mortality rates are of little value for this type of study.

Fränkel and Dublin in a study of 70,729 deaths from influenza-pneumonia among the policyholders of the Industrial Department of the Metropolitan Life Insurance Company, find that during the normal period between 1911 and 1917, influenza-pneumonia attacked primarily the first age period of life, ages one to four years, and the period of late middle life and old age. The rates are normally minimal between 5 and 30 years. In the last quarter of 1918, on the other hand, the highest rate among the whites is in the period of early adult life, between the ages of 25 and 34. There appear three modal points instead of the two at the extremes. They find that the excess over normal was most marked in infancy and early childhood, and particularly in early adult life, culminating between the ages of 25 and 34. The period of old age shows no significant _excess_ during the period of the epidemic.

If the deaths among the white males of the age period of active adult life had continued throughout the whole year as they did during the last quarter of 1918, approximately four per cent. of the population of that age would have died.

Fränkel and Dublin are of the opinion that this change in the age incidence of influenza mortality between epidemic and endemic periods suggests strongly that the two diseases are different; that endemic influenza is not the same disease as epidemic influenza. Or perhaps they should say more correctly that the diseases occurring in interepidemic times which are reported to them as deaths due to influenza-pneumonia are not the same as the epidemic influenza. They draw similar conclusions from the different manner in which the white and black races are affected during the interepidemic and epidemic periods, from so-called influenza-pneumonia. We have seen from Frost’s results that it is hazardous to compare mortality rates of different localities and different times with the idea of comparing the disease, influenza, itself.

The ages showing highest mortality in the autumn of 1918 appear to have been essentially the same as those which predominated thirty years ago. There appears to be nothing in the age distribution that could be explained by an immunity persisting over from the epidemic of 1889–93. The age group 30 to 40 has almost universally a higher mortality than the groups below 20, which would by this theory be non-immune and would be expected to have a higher rate. The drop in rate is nearer the age group of 40 than 30. The presence of smaller or larger influenza epidemics in the course of the thirty years would further complicate such an hypothesis.

_Relationship to occupation._—Dublin found in a study of 4,700 miners that the death rate was unusually high from influenza in these individuals for the last quarter of 1918. In fact in the age period 45 to 65 the rate among bituminous coal miners is close to four times as high as among all occupied males. The annual death rate per thousand for all ages among the former is 50.1; among all industrial white males, 22.3. The increase is apparent in all age groups from 15 to 65 inclusive. These results are based on the records of the Metropolitan Life Insurance Company.

_Density of population._ _Rural and urban environment._—There have been few reports which have like the above described clearly variations due apparently only to occupational differences. Some attention has been paid to a comparison of the rural incidence with that in large cities. Although other factors play a part here, we may consider this under the general subject of occupation. Statistics for the fall of 1918 from the Netherlands show that with the exception of men over 80 years of age the mortality was remarkably increased for both sexes in communities of less than 20,000 inhabitants.

Winslow and Rogers have studied the variations in the urban and rural incidence and find that in Connecticut with the single exception of Tolland County, in which the small towns were severely hit, the rates were in every case _higher_ in the large communities. In New Haven County, for instance, among nine towns which were purely agricultural, the combined death rate from influenza and pneumonia for the three months of September to November, inclusive, was 9.2 on an annual basis. For six towns in the same county in which there were manufacturing plants the corresponding rate was 15.6. In Litchfield County the twelve purely agricultural towns had a combined rate of 6.5, whereas among eleven partly manufacturing towns the rate was 18.3. This was true for other counties. The figures quoted are for influenza-pneumonia rates only up to December 1st, but study of the records during the early months of 1919 did not show any change in the figures. The rates for the entire state for January, 1919, was 19.8, and that for the towns under 5,000, only 17.5.

These observations differ somewhat from those reported by Pearl, who studied 39 large cities of the United States in an attempt to find a correlation between the explosiveness of the influenza outbreak and the density of population. He concluded that there was no such correlation. Pearl, however, was dealing with cities which were all sufficiently large to offer practically complete opportunities for contact infection, and the two reports, therefore, cannot be justly compared. Winslow and Rogers suggest as possible causes for lessened incidence in rural communities either diminished opportunities for contact infection or differences in age distribution and racial composition of the different populations.