Association of primary Pneumocystis carinii infection and sudden infant death syndrome.

To delineate clinical and histological features of the first Pneumocystis carinii infection affecting the immunocompetent host, P. carinii-specific histological stains were performed on autopsy lung specimens from 534 consecutive pediatric patients (those with AIDS and malignancies were excluded) in Santiago, Chile. P. carinii clusters were found in 4 (25%) of 16 infants who died of no apparent cause at arrival to the emergency department, and in 10 (2.9%) of 342 infants who died of multiple conditions at the hospital (P=.002, Fisher's exact test). This prompted us to analyze additional series of infants with sudden infant death syndrome (SIDS). In 161 additional SIDS cases, 47 (35.1%) of 134 infants from Chile and 4 (14.8%) of 27 infants from Oxford, United Kingdom, were found to have P. carinii clusters in the lungs. The quantity of P. carinii cysts was small compared with the numbers seen in immunocompromised hosts with P. carinii pneumonitis. This study provides histological evidence that primary P. carinii infection is associated with SIDS.