through 18 months of age is advised to document the loss of passively acquired maternal antibodies (CDC, 1998c).

Because transmission of HIV occurs primarily in utero and intrapartum, there is only limited utility in infant testing. When maternal serostatus is unknown, however, HIV antibody testing of the newborn is important for the identification of children at risk for perinatal HIV infection and early referral for appropriate medical evaluation and care. Control of viral replication and preservation of the developing immune system have been demonstrated in infants who initiated intensive combination antiretroviral therapy in early infancy (Luzuriaga et al., 1997). In addition, the initiation of prophylaxis against PCP at age four to six weeks has been recommended for all infants born to HIV-infected women; such prophylaxis should be continued until HIV infection has been excluded (CDC, 1995a).

Perinatal transmission can occur antepartum, intrapartum, and postpartum. Several factors, including maternal and virologic factors, fetal factors, placental conditions, obstetric factors and breast-feeding, may influence the risk of perinatal transmission. Recent improvements in our understanding of the timing and pathogenesis of perinatal HIV infection have allowed the development of effective strategies to prevent perinatal HIV transmission. To maximize prevention efforts, women must be identified as HIV-infected as early as possible during pregnancy and offered effective antiretroviral therapy. Postnatal evaluation of the HIV at-risk infant, beginning immediately after birth, is important for early diagnosis and optimal medical management.