A total of 2,580 sera of the patients who were consulted to the serology laboratory of the Seoul National University Hospital were collected in 1990. The sera were screened by micro-ELISA to detect IgG antibody reacting with Pneumocystis carinii antigen. The absorbances were 0.00 to 1.41 and mean 0.27 +/- 0.253. As the positive criterion was set absorbance 0.2 or more with 70% sensitivity, total positive rate was 44.4%. Mean absorbances and positive rates were higher in children than in adults; 0.40 and 62.9% in 0 year group, 0.50 and 81.2% in 1 year group, 0.41 and 66.0% in 2-3 year group, 0.33 and 61.4% in 4-5 year group, 0.25 and 42.3% in 6-10 year group respectively. In the age groups over 11 years, the absorbances were in range of 0.16 to 0.23 and the positive rates were 26.1% to 41.5%. The present level of absorbances and positive rates could be regarded similar with those in normal Korean population. The present findings suggest that most humans are exposed to Pneumocystis within 2 years after birth and meet much less new antigenic challenge after 11 years in Korea.
