Serological study of Pneumocystis carinii infection in the absence of immunosuppression.

Serum samples from 145 children with no known immunosuppressive illness were examined by indirect immunofluorescence for antibody to Pneumocystis carinii. Positive antibody titres (greater than or equal to 1:8 dilution) were found in 69 children (48%). Antibody could not be detected in the remaining children. Previous studies have shown that at least 75% of children have antibodies to P. carinii by the age of 4 years. This study shows a lower percentage of children with detectable antibody. This may be related to geographical variation of antigen or possibly to the widespread use of co-trimoxazole.