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slight, undetected, or "missed" cases, as they are called, which
are the most effectual promoting causes of an epidemic. During
the year we had several instances of these undetected cases,
giving rise to limited outbreaks in different schools. In addition
to the "missed" cases, there are other factors which render it
difficult to fulfil the essential conditions of successful isolation.
The infection must not be handed on by the patient before
seclusion, but it is not certainly known how early in the disease
the patient may be infectious. There is hardly a disease
concerning which opinions have so materially changed as
Scarlet Fever. It was formerly held that the disease was not
infectious until the skin had commenced to peel, and that it
continued infectious as long as the peeling of the skin lasted.
Both theories have been discarded. Scarlet Fever is infectious
from the commencement of the symptoms and the condition of
the skin is no criterion of the infectiousness of the patient. If
the spread of these two diseases is to be prevented, their early
infectiousness must be more clearly recognised. Moreover, the
patient should have recovered perfectly before he is cleansed
and discharged from seclusion, but in Scarlet Fever we have no
means of ascertaining whether the patient is absolutely free
from infection or not. In Diphtheria, the conditions are
different; the germ has been isolated, and a bacteriological
examination can always be made before the patient is discharged
from seclusion. In the Fever Hospital two consecutive
negative swabs are always obtained before the patient
is discharged.
The question of "return" cases is dealt with more fully in
the Annual Report of the Medical Officer of Health, but it is
mentioned here as one of the factors in the direct mode of
infection.
These matters are mentioned because during the year
there has been much controversy as to the value of daily
disinfection of the schools in the prevention of infectious
disease.