Mortality.
According to Marchese, in 1387 at Forli in Italy, not a person escaped the disease, but only a few died. Gassar says that during the same epidemic in Germany the patients suffered four, or at most five, days with the most disagreeable catarrhal symptoms and delirium, but recovered, and only very few were removed by death.
Pasquier remarks concerning an epidemic in 1411 that an infinitude of individuals were attacked but that none died.
Concerning the epidemic of 1414 in France, Lobineau relates that the disease was fatal only for the aged. Mezeray also speaks of the high mortality of the old in this epidemic.
Regarding the pandemic of 1510, Thomas Short remarks that none died except some children. Mezeray, on the other hand, says that the disease had claimed many victims.
Pasquier and Valleriola both write of the epidemic of 1557, in France, as being distinctly mild in character. Children only who could not freely cough out the phlegm died. Coyttar speaks of the absence of death except in tuberculous patients.
In the pandemic of 1580 individual observers report enormous death rates. Thus, according to Schenkius, the disease killed 9,000 persons in Rome, while Madrid, Barcelona and other Spanish cities were said to have been nearly depopulated by the disease. This high mortality was, however, even at that time attributed by some physicians to the injudicious employment of venesection. Throughout the more recent history of pandemic influenza opinion seems to have been nearly unanimous that blood letting has had very bad results in the outcome of influenza cases. Remarks to this effect have been made by the contemporaries of nearly every epidemic since 1580.
According to Rayger and others during the epidemic of 1675, nobody died of the disease itself with the exception of debilitated persons, although it spared neither the weak nor the strong.
Concerning the epidemic of 1688, Thomas Short writes for England that though not one of fifteen escaped it, yet not one of a thousand that had it died.
In 1712, Slevogt writes that in Germany “Fear soon vanished when it was seen that although it had spread all over the city, it left the sick with equal rapidity.”
Finkler remarks, concerning 1729–30, that, “The great mortality which attended the epidemic in England and Italy seems somewhat remarkable. Thus Hahn states that in London in the month of September one thousand persons died each week, and in Mayence forty persons daily. Most likely, however, other diseases which were present at the same time added their quota to the mortality, especially as the disease in other places, for example in Germany, ran a benign course.”
Perkins, Huxham, Pelargus, Carl and others, concerning the epidemic of 1732–33, all testify that the disease was of very low fatality.
In 1742 the epidemic was evidenced by an enormous morbidity but the disease was not dangerous as a general rule although Huxham occasionally speaks of the virulent character of the disease in England, and Cohansen says that in January, 1743, over 8,000 persons died from influenza in Rome and 5,000 in Mayence.
We have the testimony of Robert Whytt, for 1758, and that of Razoux and Saillant and Ehrman for 1762, as to the low mortality of the epidemic for those years.
According to Heberden the same was true for 1775, while Webster tells us for 1780 that the disease was not dangerous but its effects were seen the following year in the increased number of cases of phthisis.
Finkler remarks concerning the epidemic of 1802, “The mortality in this epidemic was small, only the abuse of venesection brought many to the grave. Thus, so many farmers are said to have died in Russia from it that venesection was forbidden by an imperial ukase. Jonas says that many patients were bled either on the advice of a simple village barber or by their own wish, and most of them died. In Prussia also bleeding was declared detrimental by the Government.”
He continues regarding 1836–37, that, “In London there died, during the week ending January 24, 1837, a total of 871 persons, and among these deaths there were 295 from disease of the respiratory organs; during the week ending January 31st, out of a total of 860 deaths there were 309 from diseases of the respiratory organs.”
Watson, in describing the epidemic of 1847, discusses the mortality:
“The absolute mortality has been enormous; yet the relative mortality has been small. You will hear people comparing the ravages of the influenza with those of the cholera, and inferring that the latter is the less dangerous complaint of the two; but this is plainly a great misapprehension. Less dangerous to the community at large (in this country at least) it certainly has been; but infinitely more dangerous to the individuals attacked by it. More persons have died of the influenza in the present year than died of the cholera when it raged in 1832; but then a vastly greater number have been affected with the one disease than with the other. I suppose that nearly one-half of those who were seized with the cholera perished; while but a very small fraction, indeed, not more probably than two per cent. of those who suffered influenza have sunk under it.”
Leichtenstern remarks on the very low mortality of 1889–90. In Munich 0.6 per cent. died; in Rostock 0.8 per cent.; in Leipzig 0.5 per cent.; in fifteen Swiss cities 0.1 per cent.; in Karlsruhe 0.075 per cent.; in Mecklenburg-Schwerin 1.2 per cent. This does not, however, include the numerous deaths from complications, as from pneumonia, and does not express the true mortality.
Newsholme gives the following table for mortality from influenza, bronchitis and pneumonia, in England and Wales during the epidemic years and the years immediately preceding them. The figures express annual death rate per million of population. The highest rate was reached in 1891. The table does not include deaths registered as from other diseases, but due directly or indirectly to influenza. Respiratory diseases in general show a greatly increased death rate in years in which influenza is epidemic. Such is also true to some extent with diseases of the nervous and the circulatory systems.
| Death rate per million of population from | Non-epidemic years. | Epidemic years. | ||||
|---|---|---|---|---|---|---|
| 1887 | 1888 | 1889 | 1890 | 1891 | 1892 | |
| Influenza | 3 | 3 | 2 | 157 | 574 | 533 |
| Bronchitis | 2,117 | 2,041 | 1,957 | 2,333 | 2,593 | 2,266 |
| Pneumonia | 1,113 | 1,093 | 1,022 | 1,404 | 1,471 | 1,250 |
In a report by the United States Public Health Service early in 1919 the death rates from all causes in twelve large cities of this country were compared for 1889–90 and for 1918–19. It was found that while considerable irregularity in the curves was evident, the curves of the two epidemics manifested on the whole quite a striking similarity for the same cities considered individually and for the group as a whole. The death rate rose to a much higher point during the autumn wave of the 1918 epidemic than in the epidemic of 1889–90 in nine out of the twelve cities. During both epidemics the rate was relatively low in St. Louis, Milwaukee and Minneapolis. The mortality in all of these cities was 26.7 in 1889, as against 35.2 for 1918. In the peak week the rate rose to 55.6 in 1918 as against 35.4 in 1889.
The influenza deaths in Massachusetts in the year 1890 during a period of fifty days were estimated by Abbott to have been 2,500. In 1918 Jordan estimates the mortality for the same state to have been six times as great. The population of the state had not doubled in the interval. The highest mortality from influenza in Massachusetts during the 1889–93 epidemic occurred in January, 1892, during which month the total deaths amounted to 6,309 which was greater by 2,246 than the mean monthly mortality of the year, and greater by more than 1,000 than the mortality of any month in the ten year period 1883–92.
A comprehensive comparison of the damage done by influenza in 1918 with the deaths from other plagues has been made by Vaughan and Palmer.
“The pandemic of 1918, when compared with that of 1889–90 is estimated to have caused six times as many deaths.
“During the four autumn months of 1918, 338,343 cases of influenza were reported to the Surgeon General. This means that in the camps of this country one out of every four men had influenza.
“The combination between influenza and pneumonia during the fall of 1918 seems to have been closer and more destructive than in any previous pandemic. During the autumn season there were reported to the Surgeon General 61,691 cases of pneumonia. This means that one out of every twenty-four men encamped in this country had pneumonia.
“During the same period 22,186 men were reported to have died from the combined effects of influenza and pneumonia. This means that among the troops in this country one out of every sixty-seven died.
“This fatality has been unparallelled in recent times. The influenza epidemic of 1918 ranks well up with the epidemics famous in history. Epidemiologists have regarded the dissemination of cholera from the Broad Street Well in London as a catastrophe. The typhoid epidemic of Plymouth, Pa., of 1885, is another illustration of the damage that can be done by epidemic disease once let loose. Yet the accompanying table shows that the fatality from influenza and pneumonia at Camp Sherman was greater than either of these. Compared with epidemics for which we have fairly accurate statistics the death rate at Camp Sherman in the fall of 1918 is surpassed only by that of plague in London in 1665 and that of yellow fever in Philadelphia in 1793.
“The plague killed 14 per cent. of London’s population in seven months’ time. Yellow fever destroyed 10 per cent. of the population of Philadelphia in four months. In seven weeks influenza and pneumonia killed 3.1 per cent. of the strength at Camp Sherman. If we consider the time factor, these three instances are not unlike in their lethality. The plague killed 2 per cent. of the population in a month, yellow fever 2.5 per cent. and influenza and pneumonia 1.9 per cent.
“In four months typhoid fever killed 1.5 per cent. of the soldiers encamped in this country during the war with Spain. Influenza and pneumonia killed 1.4 per cent. of the soldiers in our camps in 1918 and it also covered a period of four months.”
The Bureau of the Census has made the following report concerning influenza deaths in the United States:
“In forty-six American cities, having a combined population of only a little more than one-fifth the total for the country, the mortality resulting from the influenza epidemic during the nine weeks period ended November 9th was nearly double that in the A. E. F. from the time the first contingent landed in France until the cessation of hostilities.”
The mortality, even as the morbidity, has varied in different localities and at different periods. The low morbidity and mortality in the spring of 1918 has been frequently mentioned. Among the Esquimaux in Alaska the death toll was terrific. Whole villages of Esquimaux lost their entire adult population. It has been estimated that in British India the death roll totalled 5,000,000. “The central, northern and western portions of India were the worst sufferers. The hospitals in the Punjab were choked so that it was impossible to move the dead quickly enough to make room for the dying. The streets and lanes of the cities were littered with dead and dying people. The postal and telegraph services were completely disorganized; the train service continued, but at all principal stations dead and dying people were being removed from the trains. The burning ghats and burial grounds were literally swamped with corpses, while an even greater number awaited removal. The depleted medical service, itself sorely stricken by the epidemic, was incapable of dealing with more than a minute fraction of the sickness requiring attention. Nearly every household was lamenting death, and everywhere terror and confusion reigned. No part of the Punjab escaped.”
The Bureau of the Census estimates that 445,000 deaths from the epidemic of influenza occurred in the United States in the period between September 1st and December 31st, 1918. There is no doubt but that the total death toll for that epidemic exceeded 500,000 individuals.
According to Winslow and Rogers, the two highest annual death rates on record in Connecticut are both rates of 19.4 per 1,000 and these two rates are for the influenza epidemic years of 1892 and 1918. In the earlier of these two the normal general death rate was several points higher than it is today, so that the effect of the recent epidemic was much more serious than was that of its predecessor. For a single month the death toll of October, 1918, was absolutely unprecedented in Connecticut. They estimate that the epidemic between September, 1918, and January, 1919, cost the State 5.5 lives per 1,000 population, or, in all, 7,700 lives.
In the United States Army there was a total of 688,869 admissions for influenza. The total deaths ascribed to the disease are 39,731, which gives a rate of 15.64 per 1,000 for the acute respiratory diseases out of the total disease death rate of 18.81 for the year. In 1915 the per cent. of deaths from this group of infections was under 18 per cent. of the total from all diseases. During the last four months of 1918, 11,670 deaths from influenza and pneumonia occurred in the American Expeditionary Forces in France. There were approximately 1,600,000 officers and men in the United States and an equal number in France.
Carnwath gives the following comparison of the number of deaths in London and in certain American cities from influenza and all forms of pneumonia during the eight weeks of the 1918–19 epidemic.
| Deaths in London and in American cities. | ||
|---|---|---|
| Number of deaths. | Rate eight weeks per 100,000 of population. | |
| London | 13,744 | 341 |
| New York | 20,681 | 360 |
| Chicago | 8,785 | 343 |
| Philadelphia | 12,806 | 749 |
| Boston | 4,211 | 548 |
The cause of death in the vast majority of cases is some form of pneumonia. In fact it has been questioned whether influenza uncomplicated can cause a fatal issue. Postinfluenzal meningitis has been the cause of death in an appreciable number of cases. More remotely the disease has caused many deaths by hastening the fatal outcome of what were otherwise subacute or chronic conditions of the respiratory, cardiovascular, or renal systems.
Vaughan and Palmer record that, “The pandemic of influenza in 1918 seems to have been more closely associated with the pneumonias than appears in any previous pandemic. From the reports as sent to the Surgeon General’s Office, it appears that uncomplicated influenza was not by any means a fatal disease and that the high death rate was due to the pneumonias which followed. Pneumonia is a serious disease at all times. Recent records for the United States Army show that the case mortality rate for this disease has been as follows during the different periods of the last two years:
| 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 year. | 1–4 | 5–13 | 14–19 | 20–49 | 50–64 | Over 64 | Total. | |
|---|---|---|---|---|---|---|---|---|
| 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.
Let us consider in greater detail the fate of both rural and urban individuals who had been recently drafted into the military forces of this country. Almost universally the raw recruit was found more susceptible to disease than was the seasoned soldier. A report by Lieutenant W. D. Wallis from Camp Lee “shows that while those who had been in the service less than one month constituted only 9.19 per cent. of the total strength, they furnished 30.11 per cent. of the total deaths from influenza and consequent pneumonia. Furthermore, it is shown that while those who had been in the service from one to three months constituted 45.18 per cent. of the camp, they furnished 46.24 per cent. of deaths. On the other hand, those who had been in the service more than three months constituted 46.63 per cent. of the population and furnished only 23.69 per cent. of deaths.
Lieutenant Wallis says: “These figures show a much greater percentage of deaths for the first month in camp than the corresponding proportion of the population would warrant; while in the period of three months or more of service the percentage is less than half of that of the camp population having this length of service. The only approach to a correspondence is in the period from one to three months where the respective percentages differ but little. The increase in length of service is accompanied by a progressive decrease in the percentage of deaths from 30.11 per cent. to 27.41 per cent. to 18.87 per cent., although only 9.19 per cent. of the population in the camp falls within the class of less than one month’s service.
“The incidence of mortality is in the first month’s service more than three-fold the percentage of the number of men; and in the period of three months or more of service is scarcely more than half of the percentage of the number of men of the camp in that group.
“The fact that the case mortality is higher among those who came from rural homes than among those who came from cities seems to hold even after three month’s of service, or more.”
Vaughan and Palmer found that the case fatality at Camp Dix among those who came from cities with a population of 10,000 or more was 10.8; while among those who came from more rural homes the rate was 15.8, although the average service of both groups was the same.
The Camp Surgeon of Camp Grant concluded from his records that the new recruit is more susceptible to influenza and is more apt to succumb than is the man who has been trained and is accustomed to Army life.
Wooley reports data collected from four Infantry organizations at Camp Devens comprising 15,502 men. Of 9,559 men who had been in camp less than five months, 3,575 or 37.5 per cent. developed influenza, whereas of 5,943 men who had seen more than five months service in the army, 1,033 or 17.5 per cent. developed the disease. He concludes that the large number of recruits in the camp certainly was a factor in increasing the disease incidence. It should be remarked that Camp Devens appears not to have had any influenza epidemic in the spring of 1918.
It is to be regretted that we have not several reports dealing with the same subject from camps where the disease was definitely recognized in the spring. Fortunately we have one such. Opie and his co-workers have observed that the epidemic at Camp Funston, which occurred between March 4th and March 29th, 1918, and which attacked 1,127 out of a total of 29,000 men, involved chiefly the organizations which had been at Camp Funston during six months or more. At that time it seems to have infected all susceptible individuals, and to have spent itself. Subsequent waves of influenza, four in number, and coming at a little less than one month intervals, occurred when newly drafted men were brought into the camp in April and May. In these latter cases the disease affected the men newly arrived in camp.
At Camp Funston, at least, the higher incidence in the raw recruit appears to be explained in part by a relative immunity of those who had been in camp a month or more, existing as a result of an earlier prevalence of the disease. More abundant evidence would, however, be necessary before we could deny a diminution of natural immunity in the recruits, caused by the exposure, overwork, fatigue, and change of daily routine. As V. C. Vaughan has remarked: “It appears that natural immunity gives way before exposure, overwork and fatigue, as was demonstrated years ago by Pasteur in his experiments on birds with anthrax. Likewise, it is possible for human beings to have their resistance lowered by exposure to unaccustomed environment, so that although naturally immune, the standard of immunity is reduced to the point where the influenza virus gains admittance and overcomes the lowered resistance.”
Race stock and mortality.—The relationship of morbidity to race stock has already been considered and should be borne in mind in a discussion of mortality by race.
We have seen how the natives of India suffered unusually from the influenza, the total deaths being estimated at over 5,000,000 individuals. A preliminary report from the Department of the Interior on the mortality from influenza among American Indians showed that during the six months period from October 1, 1918, to March 31, 1919, over two per cent. of the Indian population died of influenza. The mortality among Indians in the Mountain States, especially in Colorado, Utah and New Mexico, was very high. For the Indian population as a whole the annual mortality rate from influenza alone during the six months period was according to the U. S. Public Health Reports 41.2 per 1,000, which is above that for the larger cities in the United States during the same epidemic period.
In both of the above races we cannot say that it was not factors other than race, particularly living conditions, that resulted in the high mortality.
Winslow and Rogers found in Connecticut that the proportion of influenza-pneumonia deaths was lower than would be expected among persons of native Irish, English and German stock, but higher than would be expected among Russian, Austrian, Canadian and Polish stock, and enormously high among Italians. They suggest that this marked difference in racial incidence may be very largely due to the differences in age distribution of the various race stocks, the races showing the highest ratios being those which have arrived more recently in the country and which are made up more largely of young adults at the ages which suffer most severely from influenza. They further refer to the work done by Armstrong in Framingham, and state that their results tend to confirm his conclusions in regard to the Italians, as do the figures presented by Greenberg from the records of the Visiting Nurse Association of New Haven. “It appears that Italy suffered very severely from the influenza epidemic in Europe, and Dublin has shown that the normal pneumonia rate of this race is a very high one.”
We have rather more abundant comparison of the white and black races in this country. Frost found in his extensive survey that the case fatality was generally higher among the colored than among the white population. A similar observation was made by Howard and Love, who found that the case mortality for influenza and its complications in the United States and in the American Expeditionary Forces, in 1918, was for colored troops 4.3 per cent. and for white troops 3.3.
These two series of observations are of great importance, for they are about all we have describing case fatality rate. The majority of other reports describe mortality rate only, and are therefore not complete.
The death rate in the Army was higher among colored troops, but the incidence of influenza, the rate per 1,000, was lower for the colored race. “Considering only the southern states, the nativity rate for influenza for the white was 247.11 and for the colored, 154.58. For lobar pneumonia it was 10.77 for the white and 28.31 for the colored; for bronchopneumonia and unclassified pneumonia 7.26 for the whites and 11.43 for the colored. It seems probable that the negro is less susceptible to influenza than the southern whites, but that he is much more susceptible to pneumonic infections, either primary or secondary.”
Fränkel and Dublin have studied the racial distribution of 70,729 deaths among policy holders of the Industrial Department of the Metropolitan Life Insurance Company, particularly with respect to incidence among white and black. Normally the mortality from respiratory diseases is higher among colored persons than among whites. In the seven year period from 1911 to 1917, influenza-pneumonia death rates showed an excess of 72 per cent. colored males over white males and of 56 per cent. colored females over white females. During the period of the epidemic the situation was reversed. The whites suffered from higher rates than the colored. While the rate among white males during the period, October to December, 1918, was nearly fifteen times as great as during the period 1911 to 1917; that of colored males was only seven times as great as the rate during the same seven year period. White females during the height of the epidemic showed a rate more than sixteen times as high as the normal, while colored females experienced a rate only nine times as high. After the first of January, 1919, the excess rate returned slowly to the normal figures. These facts are based on death rate only.
Any comparison of race morbidity or mortality, to be of value, must be based on observations of individuals living in the same climate, in the same domestic environment, and in similar age distribution. It is practically impossible to discover groups living under such conditions. Howard and Love, perhaps, approached more nearly to such an ideal in studying the white and black races in the Army, but even in the military forces many factors are at play. Thus, the death rate among enlisted men was highest among the American troops in the United States (12.02); second in Europe (6.07); third in Panama (1.09); fourth in Hawaii (0.55); fifth in the Philippine Islands (0.14). By race it was highest for the colored troops (12.69); second for the white (8.83); third for the Porto Ricans (7.80); fourth for the Filippinos (2.84); and fifth for the Hawaiians (1.72). The authors point out that while the native troops had higher admission rates than the whites, the death rates were lower, which illustrates the point that the death rate for this type of disease is lower in the summer and in the tropics.