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INFLUENZA.
Influenza in itself is not a notifiable disease in this country.
The number of notifications received in respect of one of its major
complications—influenzal pneumonia—is dealt with in the section
on pneumonia. During the year 1937 the number of deaths from
influenza was 93, of which 49 were of males and 44 of females. The
death rate per 1,000 of the population was 0.36. The corresponding
number of deaths for the years 1934, 1935, and 1936 were 24,
19, and 20 respectively; and the death rates for these years were
0.09, 0.07, and 0.11. It might be said that 1937 was almost an
" influenza year," since the number of deaths indicated that the
disease was present almost in epidemic proportions.
Influenza is one of the most baffling of diseases from the
standpoint of the epidemiologist, and it is therefore difficult to discuss
its vagaries in a short note. From Table XIV. it is immediately
apparent that the death rate has not diminished during the
last forty years, and the figures at their face value suggest that
the mortality has not decreased. This fact is partly explained by
changes in the method of allocating deaths. Whatever the statistical
difficulties, it is evident that influenza is a serious cause of
death in any five year period.
The table unfortunately starts at a period just after the passing
of the peak of a great epidemic wave, and it is seen that the
reduction in mortality was gradual. The period 1916-1920 shows
a very high mortality rate, which is due almost entirely to the
great pandemic of 1918-1919. After this event the mortality again
declined gradually. More detailed analysis of the_ figures for the
post-war years shows that smaller epidemics occurred at irregular
intervals. If we take as a rough measure of epidemic proportions
a death rate of 0.50, it is seen that the disease was prevalent to
this degree in the country as a whole in the years 1922, 1927, 1929
and 1933, and for practical purposes also in the year 1924. Applying
the same criterion to the local rates it is seen that the disease
was also present in epidemic proportions locally in the years 1922,
1929, and 1933. In 1924 and in 1927 the mortality was much less
than in the country as a whole, so that it might be said that this
area escaped some of the expected consequences of the epidemic.
It is characteristic of influenza that it spreads as rapidly as the
fastest means of human travel—whatever that may be at the particular
period under discussion. In the London area escape from
infection can sometimes be anticipated but never assured, and the
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