CHART XVI.
In the 1920 recurrence we found that 9.55 per cent., or one-tenth of the entire population, suffered from the disease, and the arrangement of districts in order of incidence was very little changed. The Irish community suffered least; the two middle class communities most. The well-to-do district in Brookline had the next lowest incidence in 1920. That the high recorded incidence in middle class districts was not due to more accurate or more thorough work on the part of the inspectors is indicated by the fact that a great part of the work on Districts IV and V was done by the same individuals who inspected Districts II and III.
One-fifth of the population studied developed the influenza in 1918–19, and one-tenth of the same population suffered in 1920.
We may agree with Winslow and Rogers, who conclude that the proportion of the population actually affected by the influenza epidemic in 1918 varied between 200 and 400 per thousand.
Relation of sex to morbidity.—Abbott concluded from his studies in 1890, that the weight of testimony appears to favor the statement that persons of the male sex were attacked in greater number and with greater severity than females. Leichtenstern reached similar conclusions. In the epidemic of 1889, the males were attacked more frequently than the females. He attributes this to two causes: first, the greater exposure to infection, and; second, the fact that strong, robust individuals are more frequently attacked.
It is amusing to compare this explanation with another found in the Medical Supplement to the Review of the Foreign Press for March, 1919. “A Spanish mission composed of Maranon, Pittaluga and Falco visited Paris last October to collect information as to the identity of the Spanish epidemic with the world pandemic of influenza. They found that the epidemics in France and Spain were absolutely identical from the epidemiologic, bacteriologic and clinical standpoint. The great majority of the severe cases in both countries occurred between the ages of 16 and 40. Both in France and Spain more females than males were attacked, which was possibly explained by the greater tendency of the former to lead an indoor existence.”
Jordan, Reed and Fink, working in Chicago, found very different results. They could discover no noteworthy difference among the pupils in high school and elementary school. The attack rate was 230 for the boys and 231 for girls. One sex was presumably as much exposed as the other.
Among the employees of the Chicago Telephone Company, on the other hand, the men were affected in considerably lighter proportion than the women (151 per 1,000 as compared with 233 per 1,000 for women). Jordan believes that the age factor was largely responsible for the difference as the women employees are as a rule of much lower average age than the men.
Frost found that with few exceptions the attack rate at all ages was somewhat higher in females than in males. The total excess of incidence in females was six per cent., which ranged from an excess of nineteen per cent. in the highest locality to a deficiency of two per cent. in the lowest. Only two of the eleven localities surveyed showed a lower incidence among females than among males.