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7
diphtheria.
VI.—SPECIAL DISEASES.
Diphtheria*
General Prevalence.—It will be seen from Table III., Appendix, that the total number
of cases reported in 1920 (464) was the highest for the ten years 1911-20, but, as will be shown
later, that total does not mean that diphtheria was (approximately) three times as prevalent
in 1920 as it was in 1911. The numbers of cases reported annually show two "peaks," the first
in 1913 (296) and the second in 1920. Since 1916 (209 cases) the cases have increased in
frequency to the 1920 maximum. During 1911-15 the annual average was 254, that for the
remaining five years being 283, an increase of nearly 12 per cent.
Comparing the totals for 1919 and 1920 with the average for 1909-13, Index Numbers of
128 and 233 are obtained, as against 125 for 1914-1918. The numbers for the two years with
the ayerage for 1914-18 as standard, are 102 and 183 respectively. In the following statement
the cases reported in each quarter of the two years are compared with the averages for the
corresponding quarters of 1914-18.

The foregoing figures indicate that the "epidemic" began in the summer of 1919 and
continued to the end of 1920. An examination of Table IV., Appendix, discloses the fact that
the incidence of the "epidemic" was not uniform on the different Wards of the Borough,
neither geographically nor as regards time distribution. The Index Numbers for the yearly
totals are :—

See and Age Incidence.—During 1914-18 the attacks among males constituted (on an
average) 46 per cent, of the total cases reported. In 1919 the proportion was 38 per cent.,
and in 1920, 41—showing that during the past two years the increased prevalence fell more
heavily on females than on males. This is borne out by the Index Numbers for the two sexes
(all ages) which were in 1919—males 99, females 159 ; and in 1920—males 189, females 275—
the averages for 1914-18 being taken as the standards. There were, also, some notable
variations in the proportion of persons attacked. Below will be found the percentage age-distributions
of the persons attacked during each of the years 1919-1920, compared with the
averages for 1914-18.

In spite of the "epidemic" children under "school-age" (0-3) were proportionately less
attacked during the two years than in 1914-18, whilst "adults" (15 years and upwards) were
more freely infected. The proportion for the ages 3-15 showed a slight decline.
The sex-age incidence can be examined in another way by using Index Numbers, based
on the averages for 1914-18. Such numbers bring out the greater incidence on females, and
on persons of the elder ages (both sexes).
* Unless otherwise stated this designation includes cases certified as "membranous" or "diphtheritic croup."