Part 18

We find that in 1918 the female sex had a higher proportion of severe cases according to our standard than did the male. This was equally true in 1920. We should emphasize here that we are not comparing only the fatal cases in the two sexes, but all classified as severe, and including fatal in 1920.

Not only was the female sex attacked in slightly greater proportion, but also the individual cases appear to have been on the aggregate somewhat more severe in that sex.

_Morbidity by age._—Before discussing the incidence of influenza in the various age periods we should explain that the charts for 1920 are based on the ages given by the individuals, and those for 1918 upon these ages, corrected by the subtraction of 15 months from the age as given. In our study of cases recurring during both epidemics the age used in the calculations is that of 1920. It is for this reason that in all of our age charts we have a first age period from zero to 15 months. Infants of less than 15 months at the time of our survey were born subsequent to the peak of the 1918–19 epidemic, and are not included in computations for that time.

The general similarity of the age incidence in the six districts studied (Charts XIX and XX) is evident. As a rule two peaks can be discerned, one falling somewhere between 15 months and 9 years, and the other between 20 and 39 years. There are individual variations in the different districts, and in Districts IV, V and VI there is a tendency toward a peak in the period 55 to 64. This, however, disappears when the total 10,000 is tabulated, when the two peaks, 15 months to 9 years, and 20 to 39, show out clearly for the year 1918 (Chart XVII).

Frost found for the same epidemic that the attack rate was highest in the age group 5 to 9, declining with almost unbroken regularity in each successive higher age group, with the exception of the groups 25 to 34, in which the attack rates were higher than in the age groups 15 to 24, but not as high as that of 5 to 9.

Both series of observations agree in finding relatively high incidence in early childhood and in early adult life.

For 1920 (Chart XVII) we find that these peaks, although present, have become decidedly less prominent, and that there is a relatively higher incidence in individuals past the age of 40 (Charts XXI and XXII). There is some tendency toward straightening out of the curve; age appears to have played a less important part, and those higher ages which were relatively insusceptible in 1918 have become more susceptible in 1920. We cannot generalize in the statement that all ages which were lightly attacked in the first epidemic were more severely attacked in the 1920 spread, because the ages from 10 to 19 are found to be relatively lower during both epidemics.

Other observations have been made regarding the age incidence particularly during the 1918 pandemic. Jordan’s figures for the October epidemic show a higher incidence among school children of ages 4–13 than among those of higher school age, 14–18. The teachers in these schools had a lower attack rate than the pupils. The pupils in both school groups were from the same section of the city and to a large extent from the same families and were presumably exposed in similar degree.

Lynch and Cumming found that of 49,140 children in public institutions the influenza rate was 412 per 1,000, while among 703,006 adults in similar institutions the rate was 263 per 1,000. These figures include children in a large number of institutions scattered throughout the United States, and would indicate that in childhood the susceptibility is much greater than in adults.

Many writers agree that nursing infants show a relative insusceptibility. However Abt records a case of an expectant mother who, within two weeks of term, developed influenza, and during the course of her illness gave birth to a baby boy, who at birth was found to be suffering from bronchitis and bronchopneumonia, but who lived for three days, finally dying of bronchopneumonia. Abt concludes from a review of all of the facts that the newly born infant had influenza and that the baby had become infected before birth.

CHART XXII.

According to Carnwath, the age incidence showed curious changes. During the 1918 summer wave the ages most affected were 15 to 45. In the winter of 1918–19 there was a considerable shifting toward the extremes of life and particularly toward the younger years. The susceptibility of young children was the subject of a special inquiry in London. Though the attack rate was below the average, the chances of recovery were less than in other age groups. Of breast-fed infants, 30 per cent. contracted the disease; of artificially-fed 54 per cent. The opposite, however, occurred in lying-in homes. An inquiry in Cheshire revealed that 25.4 per cent. of expectant mothers affected died.

Renon and Mignot have made a report on the 1920 recurrence. According to them the grip of 1920 attacked all ages, in contradistinction to the 1918 epidemic, which attacked especially the young and vigorous. One-third of their group were over 40 years of age, while some were 70 and 80 years old. In spite of this the disease remained relatively mild.

_Age morbidity in previous epidemics._—Previous to the epidemic of 1889–93, the various recorded observations regarding morbidity, and particularly regarding age morbidity, have consisted often of records made by practising physicians, and are merely estimates based upon their clinical experience and varying with the type of individual treated by them. Or else they have been records made by non-medical historians. During the 19th century, the tendency toward statistical enumeration becomes more and more prominent, but the first statistical studies of real value to the epidemiologist were made in the epidemic of thirty years ago. Statistical study must begin with this last epidemic. Observations of the earlier epidemics, while very interesting for reference and comparison, are no longer acceptable as unquestioned statements of fact. Even at the present time and with all of the emphasis that is now being laid upon statistical procedure the records are far from perfect, and it is to be hoped that in years to come the improvement will be so decided that the records even of the 1918–20 epidemics will appear crude.

Buoninsegni remarks of the 1387 epidemic that many individuals of all ages died, but the deaths were particularly prevalent among the aged.

Jacob, of Königshofen, writes that “there came a general pestilence in the whole country, with cough and influenza, so that hardly one among ten remained healthy,” and that old and debilitated persons were frequently the victims.

Balioanus tells us that the epidemic of 1404 let not rank, age nor sex escape its effect.

In 1557, according to Valleriola, the disease appeared with pestilential rapidity, and spared neither sex, nor any age, nor rank, neither children nor old persons, rich nor poor, but that it was not as a general rule dangerous; children only, who could not freely cough out the phlegm, dying.

The same story is told by Molineux, for 1693, “All conditions of persons were attacked, those residing in the country as well as those in the city; those who lived in the fresh air and those who kept to their rooms; those who were very strong and hardy were taken in the same manner as the weak and spoiled; men, women and children, persons of all ranks and stations in life, the youngest as well as the oldest.” Molineux, however, added that, “it rather favored the very old who seldom were attacked with it.”

These observations are but broad generalizations; if we pause to study the psychology of the historian we are tempted to conclude that his primary object was to impress his readers with an idea of the enormousness of the dissemination of the disease during his period. That being the main endeavor, a tendency to exaggerate for the sake of rhetoric and yet remain within the limits of truth may be considered excusable. But during the 1889–93 epidemic there was ample opportunity to compare the estimates made by the practising physicians with the later statistical tabulations. As a rule the former were higher both as regards morbidity and mortality.

In the 1830–32 epidemic an interesting observation has been made. While Kahlert says that no distinction between age, sex nor rank occurred, Leberscht stated that persons of middle age, especially women in the climacteric period, were attacked with special frequency. This is of interest in view of the findings in the 1918 epidemic. Krimer states for the same epidemic that children under 14 years of age and adults over 45 years were spared by the epidemic.

For the 1836–37 epidemic Finkler records the following: “Most of the patients were adults from 20 to 40 years of age, and of these more women than men were attacked. Curiously, however, the physicians of Würtenberg speak of the great dissemination of the disease among children.”

In 1847–48, among the adult influenza patients, there are said to have been more women than men. According to Canstatt, there were proportionately more children than adults attacked.

In 1889–90, according to Finkler, no age was spared, but persons between 20 and 50 years of age were attacked by preference. No trade was a sure protection. The course of the disease in general was favorable and also quite rapid, unfavorable only in many children during the first few years of life, in many old people, in many debilitated persons, and especially in those suffering from chest affections.

An interesting table of this kind is given us by Leichtenstern. His hospital material included 439 influenza patients, and these he carefully grouped according to age.

Age. Influenza admissions, General average of per cent. admissions, per cent.

Under 10 years 0.9 0.7

10–20 years 14.7 8.8

20–30 years 40.3 27.5

30–40 years 19.1 23.3

40–50 years 10.1 15.7

50–60 years 7.4 12.3

60–70 years 5.3 8.9

70–80 years 1.7 2.6

Above 80 years 0.4 0.2

Comby found that in Paris only the new-born were noticeably insusceptible to influenza, that children up to 15 years were attacked in the proportion of 40 per cent., and adults in the proportion of 60 per cent. Danchez believed that in families in which all the adults became ill, the little children usually escaped.

Finkler states that in the schools at Bordeaux the older children were first and most frequently attacked. Of the 248 male and female teachers in 41 schools, 153 (61.7 per cent.) developed the disease. Children up to five or six years of age at any rate seem to have been very little affected, while older children were no less susceptible than adults.

Among 47,000 cases of influenza treated by physicians in Bavaria in 1889, the various ages were as follows:

1 year 1.5 per cent. 2–5 5.4 per cent. 6–10 6.6 per cent. 11–15 7.2 per cent. 16–20 11.4 per cent. 21–30 22.2 per cent. 31–40 19.3 per cent. 41–50 12.6 per cent. 51–60 7.7 per cent. 61–70 3.6 per cent. 71–80 2.0 per cent. Above 80 0.5 per cent.

Leubuscher recorded that in Jena the proportion of cases in the individual age classes did not correspond with the figures reported from other localities. Children, and especially very young children, suffered relatively less than adults.

The following statistics of the 1889–90 incidence of influenza among school children in Cologne were collected by Lent:

Attendance. Ill of influenza. Class I–13 to 14 years of age 3,002 1,015 33.8 per cent. Class II–11 to 12 years of age 5,737 1,835 31.9 per cent. Class III–10 years of age 3,701 1,130 30.5 per cent. Class IV– 9 years of age 3,590 930 25.9 per cent. Class V– 8 years of age 2,929 822 28.0 per cent. Class VI– 7 years of age 3,388 758 22.3 per cent.

These may be compared with figures for the public schools in the suburbs of Cologne:

Attendance. Ill of influenza. Class I–13 to 14 years of age 1,609 689 42.9 per cent. Class II–11 to 12 years of age 2,885 1,094 37.9 per cent. Class III–10 years of age 1,683 626 37.1 per cent. Class IV– 9 years of age 1,758 552 31.4 per cent. Class V– 8 years of age 1,771 502 28.2 per cent. Class VI– 7 years of age 1,938 510 26.3 per cent.

The increase of disease incidence with age is apparent. Finkler’s explanation for the higher incidence among the children of the suburbs, “that the children in the country had usually to walk a greater distance to school” does not appear to be complete.

Comby found that out of 3,411 school children in Lausanne 1,840 contracted influenza. This shows a relatively high incidence in children of school age in that city.

Concerning age distribution in 1889–90 Leichtenstern remarks that the greatest morbidity incidence was in school children, adolescents and young adults, especially the last. Nursing infants were attacked in considerably less degree than any of these other ages. Also in the higher ages those above sixty were attacked in lesser degree. The greatest morbidity frequently was between the ages of twenty and forty. Abbott concluded on the basis of estimates furnished him from various institutions and individuals in the State that people of all ages were attacked but the ratio of adults was greatest, of old people next, and of children and infants least.

_Relationship of occupation to morbidity incidence._—Leichtenstern found that the only apparent influence of occupation on the incidence of influenza depended upon the liability to exposure in the various occupations. He remarks particularly on the large incidence of influenza among physicians. In contrast was the low incidence in lighthouse keepers. In 1889–90 among 415 dwellers on 51 lightships and 20 isolated lighthouses on the English coast only 8 persons developed influenza and these in four localities, and in every instance there was traceable direct communication from some other source. There is contradictory evidence as to whether individuals working out of doors are more apt to develop influenza. Certain statistics show that postmen and individuals working on railroads were attacked more frequently and earlier than others, while other statistics show that in railroads the office personnel was attacked earlier than individuals on the trains and those working on the tracks.

Abbott concluded that special occupations did not appear to have had a marked effect in modifying the severity of the epidemic. At the Boston Post Office in 1889–90, of the indoor employees, 475 in number, 25 per cent. were attacked. Of the carriers, 450 in number, 11 per cent. were affected with the disease. But there were other reports of the same period which stated that the ratio of the persons employed at outdoor occupations who were attacked was greater than that of indoor occupation.

Finkler has discussed the influence of occupation at some length:

“When we compare the statistics of the last pandemic concerning the influence of vocation, we see in the first place that those first and chiefly were attacked whose occupation compelled them to remain in the open air. This was shown especially by Neidhardt, who studied the influenza epidemic in the Grand Duchy of Hesse. His conclusions, however, were disputed by others. Thus, the prejudicial influence of exposure to the open air was not supported by the statistics of railroad employees in Saxony. Of those who were employed in the outdoor service, 32 per cent. became ill; of those employed in office work, on the other hand, 40 per cent. The statistics of the local benefit societies in Plauen show that the percentage of the sick among farm hands and builders was not greater than that among the members of other benefit societies who worked indoors. In Schwarzenberg the laborers in the forest who were working in the open air all day were affected less than others, and there was no sickness whatever in some forest districts. Lancereaux, of Paris, states that most of the railroad employees who suffered from influenza were those engaged in office work and not those who worked in the open air. The preponderance of influenza patients among the factory hands may be seen from a table prepared by Ripperger:

_A. In the open air._ Occupation. Per cent. attacked. Workmen and laborers of Niederbayern 7 Railway officials in Amberg 9 Peasants in Niederbayern 11.7 Workmen in the Salzach-Correction 20

_B. In closed rooms._ Slag mills in St. Jugbert 15 Cotton mill in Bamberg 20 Cotton mill in Bayreuth 33 Sugar factory in Bayreuth 36 Aniline works in Ludwigshafen 38.8 Cotton mill in Zweibrücken 50 Tinware factory in Amberg 60 Factory in Schweinfurth 62 Gun factory in Amberg 70 Gold beaters in Stockach 80

“Many peculiar records of how individual classes of occupation have fared are obviously to be explained by the fact that the infection manifested its action in very different degrees. Thus, among the workmen on the Baltic ship-canal only those became ill who lived in the town of Rendsburg; those who had been housed in barracks outside of the city were not affected. Of the 438 lead workers of Rockhope, which is situated in a lonely valley in Durham, all remained perfectly free from the disease during the three epidemics of 1889–92.

“Some occupations are said to afford protection against influenza. Thus workmen in tanneries, chloride of lime, tar, cement, sulphuric acid, glass, and coke works, are said to have escaped the disease with extraordinary frequency.

“We shall be compelled perhaps to agree with Leichtenstern in his conclusion that occupation and social position only in so far exert an influence on the frequency of the disease as certain occupations in life lead to more or less contact with travellers.

“Very remarkable is the proportionately small number of soldiers affected, at least in the Prussian army, where, according to the official record, the epidemic from its beginning to its end attacked only 101.5 per thousand of the entire forces.”

Comparison of morbidity by occupation necessarily includes so many variables and so many factors other than occupation that the results are decidedly unsatisfactory. An example is found in Jordan, Reed and Fink’s report of the incidence among troops in the Student Army Training Camps in Chicago. They found a strikingly different attack rate in the various groups studied. In the Chicago Telephone Exchange they ranged from 30 to 270 per 1,000, although the working conditions in the various exchanges were not materially different. In the Student Army Training Corps at the University of Chicago the lowest was 39 and the highest 398 per 1,000. The higher rate group was particularly exposed to infection while the lower, although composed of men of similar ages, living under similar conditions, were guarded to a considerable extent against contact with beginning cases.

Woolley has made an interesting observation on the effect of occupation: “The disease was no respecter of persons except that it was more severe in those who were hard workers. Those who tried to ‘buck the game’ and ‘stay with it’ showed the highest mortality rates. So, the non-commissioned officers and the nurses suffered more severely than the commissioned officers and privates.

“The annual morbidity rate per 1,000 was as follows:

For commissioned officers 261 Non-commissioned officers 208 Nurses 416 White enlisted men 568 Black enlisted men 1,130

“The annual mortality rate per 1,000 was:

For commissioned officers 69 Non-commissioned officers 83 Nurses 77 White enlisted men 145 Black enlisted men 253

“The case mortalities were:

Per cent. For commissioned officers 26.8 Non-commissioned officers 40.0 Nurses 33.3 White enlisted men 26.0 Black enlisted men 22.5

“The above figures are for the period of five weeks from August 28th to October 1st, 1918, and cover the most active portion of the epidemic, but are obviously incomplete. They are given for purposes of comparison.”

Woolley makes the observation that the organizations which spent most of the time in the open and which were therefore most exposed to the weather suffered least during the epidemic. This was particularly true in the Remount Depot.

In our work we have attempted to classify our population according to occupation along very broad lines.

“_Infant_” includes all individuals up to the age of two years. In these the exposure is limited by the fact that they are either relatively isolated at home, or when abroad, are still under relative isolation in a perambulator or under the eye of a nurse. There is relatively little commingling with the older age groups.

“_Child_,” refers to all children up to the age of school years. There is relatively much greater commingling, particularly with other individuals of the same age.

“_School_” refers to all children and adolescents who were reported as attending school.

“_Home_” includes not only the housewife, the housekeeper, but also servants and invalids; all who in their daily routine spend the greater part of the time in the home.

“_Manual Indoors_” refers chiefly to laborers in factories and includes all manufacturing occupations in which the work is of a manual character no matter what the particular branch.

“_Manual Outdoors_” refers to such occupations as ditch diggers, street cleaners, conductors and motormen, longshoremen, trucksters and teamsters, telephone and telegraph linemen, etc.

“_Retail Sales Indoors_” refers to clerks in stores and all other individuals who, working indoors, come into about the same degree of contact with the public-at-large.