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(3) In some instances the child who succumbed this time for
the first time, although others in the family had previously suffered,
was not at that time exposed to home infection by reason of his
being temporarily away from home.
(4) In 6 instances the child previously unaffected was under
one year of age at the time of exposure to infection, and in 18
instances was supposed to be one year old. The correct age of the
child at the time of exposure was unknown, and was obtained by
deducting from the age at the time of this attack the difference
between the ages of the previously attacked child to-day and his
age at the time of his attack. This could in any case give an error
approaching 2 years, so that probably in many of these cases of
children who were not infected at the time of the previous exposure,
when they were supposed to be one year old, they would at that
time actually have been under this age. Of children 8 months of
age, 80 per cent, remained unaffected on exposure ; of those 9
months, 70 per cent. ; and of those under 1 year of age, 50 per cent.
(5) In a number of instances the diagnosis of measles as the
condition from which the patient was suffering was probably an
error, in that out of the 135 susceptibles who failed to succumb
to infection by home contact , in 69 instances, although there were
1,2,3 or 4 susceptible contacts, only the one child succumbed.
This could occur from the parents' tendency to diagnose all cases
of illness occurring during a measles epidemic as that disease, in
many cases a diagnosis being made that the child was "sickening
for measles," and this would be reported to the school as the
reason for the child's non-attendance.
These figures suggest that, in this area, exposure to measles
does not give partial immunity to the susceptibles.
Progress through the family.—Where only two members
of the family were attacked, out of 272 cases, the children fell ill
on the same day in 26 instances and within two days of each other
in another 22. The commonest number of days separating the
alleged onset of the illness was 8 days, the next being 15. The
number of cases where the interval was 4 days was 15, and the to
lowing numbers represent the numbers of cases where the interva
was 5 and subsequent days:—15, 11, 12, 21, 32, 12, 11, 14, 10,
18, 12, 20, 15, 5, 5, 2, 4, 1, 2, 2. These figures are subject to the
inaccuracies of the parents' memories, and possibly in many cases
represent the time interval between the occurrence of the eruption
of the first and the onset of the illness of the second.
118 instances occurred where three members of the family
were attacked. In 20 cases the first two children suecum