AIDS: The ACTG 152 study compared AZT monotherapy with ddI monotherapy in HIV-positive children, ranging in age from 3 months to 18 years. The Data Safety and Monitoring Board (DSMB) recommended that AZT monotherapy be discontinued based on survival and HIV disease progression. ACTG 152 opened in August 1991 and included 839 children. The trial assessed the efficacy of three antiretroviral drugs as first-line treatment. Only asymptomatic children with relatively normal laboratory values were excluded, so the trial was unusually broad. There were fewer toxicities associated with ddI monotherapy than ddI plus AZT. Final results clearly support the results of ACTG 175, which found that AZT alone is not the most effective first-line therapy. Pneumocystis carinii pneumonia (PCP) is the most common opportunistic infection occurring in HIV-positive children. However, CD4 cell counts are not an effective indicator of PCP risk until the children are twelve months old. In March 1994, the National Pediatric and Family HIV Resource Center, in conjunction with the Centers for Disease Control and Prevention (CDC), revised the guidelines for pediatric care. The new guidelines recommend that all HIV-positive infants, or those born to HIV-positive mothers, be started on prophylactic treatment at the age of one month.