View report page

20
17 secondary infections occurred where the primary case
remained at home. 7 of these were single infections. In one
instance there were two secondary cases, in one three, and in
another five cases. In two other cases where the primary infecting
case could not be immediately removed, two secondary cases
occurred. The total of secondary infections, therefore, where the
primary case was at home at the time of onset of the illness of the
secondary was 19.
In the Memorandum on Closure of and Exclusion from Schools
issued jointly by the Ministry of Health and the Board of Education,
the incubation period of Scarlet Fever is given as 1 to 8 days,
and the interval between the onset of illness and the appearance
of the rash 1 to 2 days.
Whereas an interval of under 24 hours separating the onset
of illness between two cases in the house would lead to the
supposition of there being a common source of infection affecting
both, when the onset of the secondary is the next day after the
onset of the primary the presumption is very strong that the
erne infected the other. Of the 31 cases which occurred secondarily
to a primary case which was removed to hospital, the number of
cases in whom the onset of the disease in the secondary was within
24 hours of the removal of the primary was 14; of those within
another 24 hours 4; and a further 7 in the next 24 hours. That
is to say, in 25 cases out of the 31, the onset was within 72 hours
o1 the removal of the infecting source. Another three fell within
the limit of the 8 days of period of incubation, leaving only 3
outside this period, the interval separating the onset of the illness
from the removal of the infectious patient being in these cases, 8,
11, and 11 days.
Of the 89 secondary infections therefore, in practically every
one the primary infecting case was presumably the source, acting
by direct infection, without invoking the hypothesis of indirect
infection by inanimate articles. Even in the case of those whose
onset was outside the incubation period from the time of removal
of the infecting source, it is not always necessary to ascribe infection
to fomites. At times, the time of eruption of the rash is given as
the onset of the illness, whereas, in the case of adults particularly
the eruption may not appear for a number of days from the true
onset as determined by the development of faucial involvement.
Further, an incubation period is not always a definite time in that
infection might lie dormant for a period until some constitutional.
factor upsets the balance in favour of the invading organisms
Before the bacteriological nature of infections was appreciated
much stress was laid on aetiological factors as the reason for