Background. Pneumocystis carinii pneumonia (PCP) remains a common and often fatal opportunistic infection among children infected with the human immunodeficiency virus (HIV). HIV-infected infants between three and six months of age are particularly vulnerable. Current guidelines recommend prophylaxis in children from birth to 11 months old who have CD4+ counts below 1500 cells per cubic millimeter. Methods. We used national surveillance data to estimate the annual incidence of PCP among children less than one year old. We reviewed the medical records of 300 children given a diagnosis of PCP between January 1991 and June 1993 to determine why treatment according to the 1991 guidelines for prophylaxis against PCP either was not given or failed to prevent the disease. Results. In our study the incidence of PCP in the first year of life among infants born to HIV-infected mothers changed little between 1989 and 1992. Among 7080 children born to HIV- infected mothers in 1992, PCP developed in 2.4 percent. Of 300 children with PCP diagnosed from January 1991 through June 1993, 199 (66 percent) had never received prophylaxis, and for 118 of those children (59 percent) exposure to HIV was first identified 30 days or less before the diagnosis of PCP. Among 129 children less than one year old, the CD4+ count declined by an estimated 967 cells per cubic millimeter (95 percent confidence interval, 724 to 1210 cells per cubic millimeter) during the three months before the diagnosis of PCP. Among infants in whom CD4+ counts were determined within one month of the diagnosis of PCP, 18 percent (20 of 113) had at least 1500 cells per cubic millimeter, a level higher than the currently recommended threshold for prophylaxis. Conclusions. In the United States the incidence of PCP among HIV-infected infants has not declined. If this infection is to be prevented, infants exposed to HIV must be identified earlier, and prophylaxis must be offered to more children than the guidelines currently recommend.
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