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44
been here 6-12 months, 18-24 months, etc. Such influence
however, is not reflected in the graphs, though possibly accounting
for some of the irregularities. Another cause for
irregularities is the alteration in the incidence rate for those
diseases obtaining in the country as a whole, this figure varying
in the last eight years for Scarlet Fever, from 2.1 to 36.
and for Diphtheria from 1.0 to 1.7 per thousand person
living.
Comparing the curves for Scarlet Fever and Diphtheria
then, apart from the difference in respect of those who had been
here less than one month, the curves are essentially similar,
showing that whatever influences are at work in the causation
of one disease are also operative in the other.
Considering them from the end of the shortest periods,
there is for the first month an incidence in the case of Scarlet
Fever well above the average, whilst the incidence is more
normal in the case of Diphtheria. This excess incidence in
the case of Scarlet Fevler is due to illness contracted in, or
associated with, the district whence the patients came, and on
deducting the figure representing these cases, the curves become
nearer the average.
Incidence in the next month is in both diseases below the
average, but after that rises to maximum for the next six months
continuing for the ensuing 12 months to higher than nornnl
After this it falls and gradually becomes less than normal
The low rate in the early months agrees with what is found
on analysing the incidence of cases on each section, viz:that
there is preliminary period of some months before local
influences become operative. It seems then, that it is persons
who have been here 5 to 17 months who contribute to our
excessive rate for these diseases. The gradual fall to below
normal occurring afterwards can be interpreted as due to
insusceptibility through immunisation brought about by the
appearance of the disease in the earlier periods of stay-
The effect of houses on the incidence of Diphtheria then
would seem to be remote.
Diphtheria.
213 cases of Diphtheria per 67,500 is at the rate of 3.16
per thousand living, compared with 1.55 for the country as a
whole. The figures of incidence per 1,000 under 15 are 1.29
times that of the country as a whole.
Of the 213, 209 were removed to hospital, those 4 remaining
at home in suitable circumstances at the parents' request.