Objective. To determine the effectiveness of primary prophylaxis in preventing Pneumocystis carinii pneumoni (PCP) in children with perinatally acquired human immunodeficiency virus 1 (HIV-1) infection.

Methods. We conducted a retrospective analysis of a cohort of infants followed from birth at six metropolitan hospitals and one outpatient clinic for pregnant, drugusing women in New York City. Outcomes measured were histologically confirmed PCP and/or death. The potential confounding effect of the infant's stage of illness, as determined by CD4 count, was controlled by including all CD4 determinations as time-dependant covariates in a Cox proportional hazards analysis. Cases were censored at PCP onset, death, loss to follow-up, and 18 months of age.

Results. One hundred twelve HIV-infected children were enrolled at birth between 1986 and 1993. Sixty of these were tracked beyond 18 months of age; of the others, 21 died before this age, 4 were considered lost to follow-up, and 27 had not reached 18 months of age at the last visit. Only 3 cases (4%) of confirmed PCP occurred among the 70 children who received primary PCP proprophylaxis before 18 months of age, compared with 12 cases (28%) among 42 children not receiving PCP prophylaxis at any point before 18 months of age. The Kaplan-Meier estimated incidence of PCP in the first year among children not receiving prophylaxis was 25% (95% confidence interval [CI], 12 to 39). Using Cox methods, the unadjusted risk of PCP among infants not receiving prophylaxis, relative to those receiving it, was 4.1 (95% CI, 1.1 to 15); the relative risk was 4.4 (95% CI, 1.2 to 17) adjusting for the percentage of CD4-positive lymphocytes and 5.1 (95% CI, 1.3 to 20) adjusting for the absolute number of CD4-positive cells. Eight of 26 deaths were caused by PCP, and the likelihood of early death was significantly diminished if PCP prophylaxis was given (relative risk controlling for absolute CD4 cells, 2.57; 95% CI, 1.1 to 6.1).

Conclusions. We report evidence that primary antimicrobial PCP prophylaxis is highly effective in decreasing the frequency of PCP and early death in infants with perinatal HIV infection. These findings support the evised National Pediatric HIV Resource Center and Centers for Disease Control and Prevention guidelines for PCP prophylaxis in children.

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