Estimating the Timing of Mother-to-Child Transmission of Human Immunodeficiency Virus in a Breast-Feeding Population in Kinshasa, Zaire

During October 1989-April 1990 at two large hospitals in Kinshasa Zaire 342 HIV-infected women were enrolled in a prospective study designed to estimate the time of mother-to-child transmission of HIV to breast-feeding infants. The women delivered 323 live-born infants (including 7 sets of twins) and 8 stillbirths. The infants were monitored on average for 18 months. HIV serodiagnostic tests used included polymerase chain reaction (PCR) HIV culture or ELISA. 69 (26%) of the 261 infants with sufficient data for determination of HIV status tested positive for HIV. Among the HIV-infected infants 23% acquired HIV during the intrauterine period 65% during the intrapartum/early postpartum period and 12% during the late postpartum period. The estimated risk was 6% for intrauterine transmission 18% for intrapartum/early postpartum transmission and 4% for late postpartum transmission. It is suggested that breast feeding was the risk factor for late postpartum transmission of HIV. These findings show that most vertical transmission of HIV occurs during labor and delivery or in the early postpartum period. Nevertheless there is a considerable risk of HIV transmission related to breast feeding during the postpartum period.