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home 12 were followed by 15 secondary eases in the same house;
of these, however, 6 began within seven days of notification and
were therefore almost certainly infected before isolation commenced,
and would have occurred just the same if the first case
had been removed to hospital. Of the remaining 9 secondary
cases, one occurred four months after notification of the primary
case, and three months after completion of isolation of this ; it
was doubtless independent of the primary case—a coincidence
only.
One occurred eight days after cessation of isolation of the
primary case; this must be looked on as a 'home return case'
i.e., infected by the primary case after the latter was supposed to
be free from infection; the primary case had been isolated for six
weeks and four days; a third case began in this house after the
secondary case.
The remaining six secondary cases occurred from 10 to 20 days
after commencement of isolation. It cannot be said with any
assurance that these were all due to failure of isolation as it is
well known that the incubation of scarlet fever is, occasionally, as
long as three weeks and longer. Thirteen cases last year removed
to Hospital were followed by secondary cases at intervals of 7 to
23 days after removal. It would, however, be reasonable to
attribute the majority of these to insufficient precations being
taken. It may then be said that home-isolation was followed by
two return cases and four secondary cases, due to failure of
isolation, or 5 per cent, of failure.
These results are not unfavourable when the general advantages
of home isolation are considered. The 12 houses contained an
average of 3j adults (over ten) and 3¼ children (under ten).
43. Other Sotirces in Injection.—In 41 cases, infection was
attributed to other members of the family. Some of these were
never notified and had no distinct symptoms of scarlet fever, but
a history of sore throats made it probable that they had had a
slight attack of this disease.