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also serves to lessen the value of a comparison between the local
rates and those for the country as a whole. Diphtheria is not at
its maximum incidence throughout the country in any one year,
and the rates for England and Wales therefore tend to show less
marked variations than do the local rates. It is nevertheless significant
that the local rates are often almost double the national
rates. This excess incidence is partly accounted for by the urban
nature of the local community.
The death rates reflect a more satisfactory state of affairs.
In the early periods covered by Table VII. deaths from diphtheria
were often attributed to other diseases, and consequently the
mortality was comparatively low. The true mortality from this
disease is apparent in the period 1891-1900, when it averaged over
0.6 per 1,000 of the population. Improvements in treatment,
especially the introduction of antitoxin treatment, led to a progressive
reduction in mortality, and the average rate during the
last fifteen years is only about one-sixth of the rate for the closing
years of last century. It should be noted that until the post-war
period the local rates were often more than double the national
rates, but that within recent years this difference has tended to
disappear. Locally there has been no significant difference in the
rates for males and females respectively, and this similarity in
the effects of the disease on the two sexes is borne out by the
national rates.
An instructive demonstration of the results of efficient treatment
in this disease is given in column 6 of Table VI. It will be
seen that the fatality rate in the pre-antitoxin era was very high,
and that a quarter or more of all affected persons died. Since the
closing years of last century this rate has decreased rapidly and
progressively—with the exception of the rate for the years 19311935.
The excess fatality in this period was caused by the very
high rate in 1933, and by slightly lower rates in the two succeeding
years. I have so far not obtained any direct bacteriological
evidence on this point, but there appears to be no reason to doubt
the fact that these high rates were caused by the introduction of a
new and very virulent strain of the organism into the community
in the year 1933, and it is probable that the strain was the gravis
strain, which was then prevalent in certain other cities. This
occurrence points to the fact that no definite conclusion should ever
be drawn regarding the future behaviour of this disease.
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