Postnatal transmission of human immunodeficiency virus type 1 from mother to infant. A prospective cohort study in Kigali, Rwanda.

Although transmission of human immunodeficiency virus type 1 (HIV-1) from mother to infant has been well documented during pregnancy and delivery, little is known about the possible transmission of HIV-1 during the postnatal period. We conducted a prospective cohort study in Kigali, Rwanda, of 212 mother-infant pairs who were seronegative for HIV-1 at delivery. All the infants were breast-fed. The subjects were followed at three-month intervals, with Western blot assays for antibodies to HIV-1 and testing of mononuclear cells by a double polymerase chain reaction (PCR) using three sets of primers. To evaluate potential risk factors, each mother who seroconverted was matched with three seronegative control women. After a mean follow-up of 16.6 months, 16 of the 212 mothers became seropositive for HIV-1. Of their 16 infants, 9 became seropositive. One infant was excluded from the analysis because of a positive test by PCR on the blood sample obtained at birth. Postnatal seroconversion to HIV-1 occurred in four of the five infants born to the mothers who seroconverted during the first 3 months post partum, and in four infants of the 10 mothers who seroconverted between month 4 and month 21. In all cases, the infant seroconverted during the same three-month period as the mother. The main risk factor for maternal seroconversion was being single. HIV-1 infection can be transmitted from mothers to infants during the postnatal period. Colostrum and breast milk may be efficient routes for the transmission of HIV-1 from recently infected mothers to their infants.