Mother-to-child transmission of HIV: implications of variation in maternal infectivity.

ABSTRACT

PIP: By 2000, an estimated 5 million children will have been infected with HIV, the majority of them in sub-Saharan Africa. 30-50% of such infections could be the result of mother-to-child viral transmission through breast-feeding. Findings are presented from a study conducted to examine the implications of variation in maternal infectivity upon the timing of mother-to-child HIV transmission through breast-feeding. A mathematical model of mother-to-child HIV transmission was developed which incorporates the possibility of the fetus/child being exposed to HIV in utero, during the intrapartum period, and through breast milk; and variation in maternal infectivity. The model was estimated from epidemiological data drawn from a retrospective cohort study of children born to HIV-1-infected women in Sao Paulo State, Brazil, the International Registry of HIV-Exposed Twins, and the AIDS Clinical Trials Group 076 trial, which assessed the effectiveness of zidovudine in preventing mother-to-child HIV transmission. The effect of duration of breast-feeding upon the overall probability of mother-to-child HIV transmission, and therefore the age-specific risk of breast-feeding-related transmission, is highly sensitive to the degree of variation in infectivity. When substantial, the average risk of breast-feeding-related transmission declines rapidly with age and most infections occur in the early stages of breast-feeding. When the variation is less, infections attributable to breast-feeding are more evenly spread across the period of exposure to breast milk, although an imbalance towards early transmission remains.