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37
As to the efficacy of removal in preventing secondary cases,
the following figures are of interest:-

The Table shows there is a steadily increasing risk of
secondary infection the longer the primary case remains at
home.
Amongst these cases however, are 5 whose onsets vary from
10 to 24 days after the removal of the first case. It is probable
that one of the other children present in the house formed a
connecting link and that there was a secondary infection which
was not prevented by the removal of the primary case to
hospital, and this secondary gave rise to the third case which
ws recognised.
In udging the value of removal to hospital as a preventive
of spread of infection, Return Cases must be taken into consideration.
These are cases occurring in the same house or
elsewhere, and apparently traceable to the person released
within a period of not less than 24 hours and not more than 28
days after his return.
Ten patients on discharge from hospital gave rise to 12
Return Cases, the interval between the date of discharge of
the infecting case, and the onset of the Return Case varying
between 3 and 22 days. 3 of the infecting cases were readmitted,
they having developed a nasal discharge on return
home.
Comparing the two sets of cases therefore, in the home
treated, of the 45 primary cases which were home treated, 6
occurred in the earlier part of the year when accommodation
was available and were allowed to remain home because of
favourable home circumstances. The other 39 remaining at
home were those selected. The average population at risk (i.e.
of children under 15) in these houses was 2.5, giving a total