Influenza : $b An epidemiologic studyVaughan, Warren T. (Warren Taylor)
History
Influenza : $b An epidemiologic study
Vaughan, Warren T. (Warren Taylor)
Influenza
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.
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