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40
Amongst the etiological factors concerned in the production
of Diphtheria, is frequently placed dampness of houses
This estate is of very rapid development and houses are
occupied within a very short time of their completion. Any
inlluence of dampness as a cause of Diphtheria should therefore
be apparent.
Graph 2 consists of three curves showing: —
1. The total number of Estate houses at the end of each
year.
2. The number of persons who have been in the area for
varying periods before contracting Diphtheria (only
primary cases on the Estate are dealt with).
The periods selected are under one month, 1-2-months
and thereafter every six months.
The figures for the shorter periods are multiplied by
the necessary factor for them to be represented on the
same scale as the curves for other periods.
3. The number of persons who were, at the time they contracted
Diphtheria as primary cases, living in houses
which had been erected for varying periods, the same
periods being selected as for the other curves. These
curves 2 and 3 will differ slightly, owing to: —
(a) A certain amount of transfer taking place on the
Estate, so that persons who have been in this locality
for some years, may be occupying a new house.
(b) Similarly, a new comer to the district may be occupying
an old house.
(c) Children born here will not be the same age as the
house they are living in.
These factors result in a smoothing out of curve 2 compart
with 3, suggesting that the causes lie in the persons more than
in the houses, and that the "house" curve is only a reflection
of the "persons" curve.
If the incidence of the disease were merely a function
of the actual population, the "persons" curve should run
parallel to the " development " curve of graph 1. On comparing
the two however, it is seen that they differ. The earl)
rise is slow but becomes rapid, the maximum slope being
evident from the period of 5 to 15 months. After this there
is a sharp fall to the second month, followed by a rise to t
first.