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war and in which, in common with many other districts, there was during
the war years such marked movement of the population, it must be a
very long time before any such regular periodicity of any of the infections
will show itself. For many years, the severity of this infection has waxed
and waned. For a number of years now the type prevailing in Northern
Europe and in America has been mild, a marked contrast to that common
in this country in the XVIIIth century and in the early part and in the
third quarter of the XlXth and which prevailed in parts of Europe just
before the war. Some saw in the removal to isolation hospitals of the
more severe cases the reason for this change in the character of the illness ;
but this suggestion ignored the previous history of the disease. What
has happened in scarlet fever is probably entirely the result of a change
in the organism, and no credit for it can be claimed by those in the Public
Health Service. Some diseases have a marked seasonal incidence. Unfortunately,
so little is known as to what the factors are that bring about
the increased prevalence at certain times or a lowered incidence at others.
In the same way, little is known of the reason that a disease takes on an
epidemic prevalence in some years, or for parts of years, and is comparatively
light in incidence at other times. The organism seems to vary
both in toxicity, with resulting change in the clinical severity of the
disease produced, and in dispersibility so that one variety of the germ will
cause the disease to spread freely while the illness caused by another
variety passes from one person to another only with difficulty. Because
a sufferer who is severely ill is usually confined to bed and so is unlikely
to spread infection to others than his immediate contacts, unless the
dispersibility of the organism changes or unless other factors such as
meteorological changes or changes in the nutritional state of the population
are present, then the disease is less likely to spread. Conversely,
it is more likely to do so if the type of illness resulting from infection is
mild. This was the case some 20 years ago when the mild variant of smallpox
spread so widely throughout the country, as contrasted with the
very limited spread of the classical type of smallpox. But mildness of
attack does not invariably result in a higher incidence. This was the
position last year, when there were in this district only 181 confirmed
cases of this infection, an incidence rate per thousand population of 0.82.
The only year with a corresponding freedom was 1947, when there were
180 cases, an incidence per thousand population of 0.83. The incidence
last year in the country as a whole was 1.11 per thousand population.
Characteristically, the incidence of scarlet fever in this country
increases throughout the summer to reach a maximum in October or
November, after which there is a fall to a minimum in March or April.
In this district, cases were most common in 1951 in March to May with
a weekly average of five cases; for the rest of the year the incidence was
particularly low, there being no cases at all notified in two weeks in the
middle of September and only one case in each of ten weeks from the
beginning of August to the end of October.
53 patients were removed to isolation hospitals, most to the Hendon
Isolation Hospital, but seven to others.
There were ten households in which secondary cases occurred.
In nine there was only the one secondary case; but in one house three