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193
Effect of nursery size and turnover
It was hoped that some information might be forthcoming on the manner in which
the size of the nursery and the relative number of children admitted during the year per
nursery place affected the amount of sickness in the nursery. In the event, as only two
nurseries were included in the survey this proved impossible.
From Table (iii) it is seen that the incidence of sickness at the two nurseries judged
by children sick and spells of sickness per 100 children was roughly equal. It is a common
experience that the rate of sickness is greater in a large institution than a small one:
moreover, one would expect the sickness rates to be higher in a place that had a high
turnover per nursery place. Whether these factors operated during the survey period
it is not possible to say because the roughly equal sick rates in the two nurseries may be
the result of two opposing forces, viz., the increased size of the Downs nursery making
for higher sickness rates, and the slower turnover at that nursery (see last column of
Table (i)) producing lower sickness rates.
Spread from one unit to another
At St. Margaret's nursery the children were accommodated on two floors each of which
was organised independently with separate staff. At the Downs nursery the children
were housed in two separate blocks, each with its own staff, for the greater part of the
time of the survey. Towards the end of the second year one of the blocks was closed,
so there was no further opportunity of block to block spread.
It is the practice when infectious disease occurs to cease to admit or discharge
children from the affected block or floor and to continue admission and discharges to
the unaffected block or floor. The justification for limiting quarantine in this way
rests upon the assumption that infection can be contained in the one block or floor.
Considerable interest therefore attaches to the evidence on this subject in the present
survey.
Secondary cases were defined as those cases of the same disease occurring in the
period between the minimum and maximum serial interval after a primary case.
In Table (v) it is seen that, excluding in the case of the Downs nursery the period
in which only one block was open, there were during the survey 105 outbreaks at
St. Margaret's and 99 at the Downs. At each nursery about a third of the outbreaks gave
rise to secondary cases. Only 5-6 per cent, of the outbreaks at either nursery spread
between blocks or floors. The policy of stopping admissions and discharges to the affected
unit appears to be abundantly justified by these figures. The diseases which did spread
from floor to floor at St. Margaret's nursery were chicken-pox (a most infectious disease),
gastro-enteritis on three occasions only out of 46 (this being quite a creditable result in
view of the high infectivity of the E. coli serotypes) and tonsillitis once. At Downs
nursery inter-block spread occurred with measles (another most infectious disease),
tonsillitis, glandular fever, ringworm and common cold.
Sources of introduction of infection
Whenever a primary case of infectious disease was discovered in either nursery an
attempt was made to find the source of the infection. Of 232 primary cases a source
outside the nursery was discovered in 38 (16 per cent.). In 29 of these cases the source
was in the child's home, and in 7 it was in a hospital from which the child was
admitted to the nursery. The origin of the remaining 194 cases was never found. Sometimes
it is suggested that children known to have been in contact with infection should
be isolated in order to prevent the introduction of infection. It is obvious from the
figures given above that only a very small part of the introduced infection is susceptible
to prevention in this way. Unfortunately, it is not possible from the data in this survey
to find out what proportion of the children known to be in contact with infectious