Streptococcal infections among children in a residential home: II. Potential sources of infection for individuals

1. For each case of streptococcal illness—sore throat, otitis, or other respiratory tract illness—observed in a 30-month study in a large children's home an attempt was made to enumerate the infected contacts from whom the infection might have been derived. 2. Of 459 illnesses, 10·5% seemed to be relapses of a previous illness, and in 10·0% the child was known to have been carrying streptococci for more than 7 days before sickening, so that the causal relation of the streptococcus is in doubt. 3. Of the 365 other illnesses, 31·5% could be attributed with varying degrees of confidence to infection from one specified carrier, 36·8% could have been derived from one or more recognized contacts although there was not sufficient evidence to specify one in particular. For 17·5% no infected contacts were recognized, but infection with the particular streptococcus was known to be present in the community; and for 9·3% there were no contacts and the streptococcus was not known to be present in the Village. 4. Of the ninety-four illnesses for which the source could be specified as one particular carrier, 66% were derived from heavy nasal, 19% from light nasal, and 15% from throat carriers. Persons incubating a streptococcal illness and healthy carriers were each responsible for 31% of the illnesses and convalescent carriers for 38%. 5. It seemed that at least 50% of all illnesses could have been contracted from contacts within the cottage; the proportion due to school infection was much more difficult to estimate but was at least 12%.