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20
In the above series is given the age incidence during the four
years whilst notification was in force. There is possibly some
error or omission dependent on the fact that notification depends
on the presence of the disease, and also on whether life i's
threatened or not, and as that risk decreases as the child gets
older, it may be reasonable to expect that the notifications at the
earlier ages more closely reflect the age incidence at that time.
Still in spite of these factors it is obvious that the age incidence
has changed in the four years under consideration, a fact that
must lie due to, firstly, the susceptibility of the population has
altered owing to previous attack, or secondly, the organism has
changed in character.
Now with respect to the first, there are certain categories to
which this cannot apply. Thus, the children of one year and
under in 1917 and 1918 are not in any way different from the
group of a similar age in 1916, and the same applies, in a lesser
degree, to those under two in 1918, yet the proportional number
attacked is different. It may, however, be contended that owing
to the rising immunity of the older children, the chance of infection
being introduced into the home has decreased. That will
not explain why the epidemic as a whole caused considerably
more discomfort in 1917 than in 1916, and yet the relative number
attacked under one year was less in 1917 than in 1916.
Unless we assume that the organism has changed during the
course of the year, we are led into considerable difficulty.
Pneumonia and Influenzal Pneumonia.
This disease became notifiable during the year, and 73 cases
were reported. The order was, of course, dependent upon the
epidemic of 1918-1919. Although sporadic cases are still occurring,
it is hardly likely to rise to any high level for a number of
years. It is possible now to form a fair estimate of the proportion
attacked during the epidemic.
The figures are estimates and are based on information derived from various sources :—