Search for primary infection by Pneumocystis carinii in a cohort of normal, healthy infants

To determine whether Pneumocystis carinii is associated with clinical illne ss in the competent host, 107 normal, healthy infants were enrolled in a 2- year prospective cohort study in Chile. P. carinii was identified by specif ic stains and nested-deoxyribonucleic acid (DNA) amplification of the large subunit mitochondrial ribosomal ribonucleic acid gene of P. carinii f. sp. hominis, and seroconversion was assessed by enzyme-linked immunosorbent as say of serum samples drawn every 2 months. P. carinii DNA was identified in nasopharyngeal aspirates obtained during episodes of mild respiratory infe ction in 24 (32%) of 74 infants from whom specimens were available for test ing. Three (12.5%) of those 24 infants versus 0 of 50 infants who tested ne gative for P. carinii had apnea episodes. Seroconversion developed in 67 (8 5%) of 79 infants who remained in the study by 20 months of age and occurre d in the absence of any symptoms of disease in 14 (20.8%). The study indica tes that P. carinii DNA can be frequently detected in healthy infants, and it raises the hypothesis that they may be an infectious reservoir of P. car inii in the community. Further investigation is needed to identify whether P. carinii causes overt respiratory disease in infants.