Determinants of mother-to-child transmission of human immunodeficiency virus type 1 infection in a cohort from Durban, South Africa.

OBJECTIVES: To determine the vertical transmission rate of HIV-1 infection and to assess the influence of maternal risk factors on transmission in infants born to HIV-1-infected black women in Durban.
DESIGN: A prospective, hospital-based cohort study conducted at King Edward VIII hospital, Durban. HIV-1-seropositive women were enrolled into the study, and their infants were followed up at regular intervals from birth to early childhood. The infection status of the children was classified and the transmission rate was computed according to the recommendations of the workshop held in Ghent, Belgium (1992).
RESULTS: The final cohort of 181 infants were classified as 48 infected, 93 not infected and 40 indeterminate. Clearance of maternal antibodies was achieved by 12 months of age in virtually all infants who became seronegative. The intermediate transmission rate was 34% (95% confidence interval, 26 to 42). Deliveries by cesarean section had significantly lower transmission (relative risk, 0.46; 95% confidence interval 0.23 to 0.91). Women with lower hemoglobin concentrations during pregnancy (< 10 g/dl) had an increased risk of transmission (relative risk, 1.99; 95% confidence interval, 1.18 to 3.34). Advanced maternal age, multiparity, positive syphilis serology, duration of ruptured membranes, preterm delivery and breast-feeding were not associated with an increased risk of transmission.
CONCLUSIONS: This study, the first from South Africa, has confirmed that the rate of vertical transmission of HIV-1 is as high as that reported from most African cohorts. Cesarean sections were protective against transmission, whereas low hemoglobin values values were associated with an increased risk of transmission. Twelve months could be used as the cutoff age for teh diagnosis of vertical infection using antibody tests.