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54
even being harmful. During the time he is excluded from school
to avoid the risk of infecting his fellow scholars, he is more likely
to come into contact at home or elsewhere with those of under
school age, children of ages at which many diseases are more dangerous
than in the case of school children and, moreover, contact in
such circumstances may be closer and more prolonged than would
occur at school.
Secondary Infections.
Secondary infections occurred in 24 households, in 21 of
which there was only one secondary case: in 2 there were two, and in
one there were four.
In 9 of the households the primary case was nursed at home.
In three of these the primary case was missed, the intervals
separating the onset of illness of the primary and of the secondary
case being 5, 12 and 17 days. In two cases where the interval
was only 2 days presumably the secondary case had been infected
before isolation of the primary case. In regard to the other
secondary infections the intervals were 10, 12, 16 and 16 days. In
these four cases it is to be presumed that, had the primary case
been removed to hospital, the secondary infections would not
have occurred. In the case of two, the secondary patient was a
mother nursing the original patient. In assessing the value of
removal to the isolation hospital of scarlet fever patients with
the object of preventing spread of infection, these 4 secondary
infections occurring in households in which were nursed 106
primary patients must be weighed against the 24 return cases
which occurred in 20 households on the return home of 306 patients
treated in the isolation hospital for scarlet fever. It is appreciated,
of course, that one of the factors determining the decision to
remove a case to hospital is the number of susceptible contacts
in the home, and that there will actually be a higher population at
risk in each household where a return case occurred as compared
with those in which the secondary infections took place.
Removal of the primary case to hospital did not prevent the
occurrence of secondary infections in a number of cases because the
secondary patient was already infected before the illness was
diagnosed in the primary case. In 8 instances the secondary case
was diagnosed at the same time as the primary and the patients
removed together. The intervals separating the onsets of illness
were 1 day in one instance, 2 days in 3, 3 days in 2, and in two
other cases 9 and 15 days. In each of these later cases the
diagnosis of illness in the second led to the recognition of the
disease in the primary case. A missed case of longer duration
caused one secondary infection in one house, 2 in another and
4 in a third, in each case in this last household the onset of illness
of each patient being either before or within 24 hours of the removal
of the infecting case. In another household one secondary case
occurred this year, infected probably by a missed case, as he was