A remaining significant challenge in resource-limited countries is transmission of HIV through breast-feeding. Infected women in such settings have a significant dilemma: breast-feeding, although it provides substantial health and survival benefits to the infant and contraceptive, economic, and social benefits to the mother, is associated with risk of HIV transmission to the infant. Avoidance of all breast-feeding is the most reliable way to prevent postnatal transmission of HIV, and this is recommended in settings in which commercial infant formula is affordable and sustainable, clean water is widely available, hygiene and sanitation conditions are good, and deaths due to diarrhea and other infectious diseases are relatively uncommon because of adequate preventive and curative health care. This is not the case in much of the world.
SAINT, which included both formula-fed and breast-fed infants, has significantly contributed to our understanding of HIV transmission through breast milk. In SAINT, all infants received effective prophylaxis against intrapartum HIV transmission; in this context, breast-feeding was the most significant risk factor for MTCT. By age 8 weeks, breast-feeding accounted for an increase in the absolute risk of transmission of ∼6%; in multivariate analysis, there was a 2.2-fold increase in HIV infection among breast-fed versus formula-fed infants during the first 4 weeks of life and an additional 7.9-fold increase between ages 4 and 8 weeks.
Similar data from a randomized clinical trial of breast-feeding versus formula feeding in Nairobi, Kenya, indicated that approximately two-thirds of transmission through breast milk occurred during the first 6–8 weeks of life, with 75% occurring by age 6 months. In this issue of The Journal of Infections Diseases the Kenya investigators report that, although viral shedding occurs throughout lactation, virus loads in colostrum and early milk are significantly higher than in mature breast milk, providing a possible explanation for the apparent higher risk of infant infection during the early breast-feeding period. Thus, although the risk of HIV transmission through breast milk persists for the duration of breast-feeding, the period of highest risk appears to be the first months of life. This is also the period during which breast-feeding provides the infant with maximum health benefits, in terms of infant nutrition and protection against diarrheal and respiratory infections. A number of ongoing and planned clinical trials will address whether short-course antiretroviral drugs given to the mother (including highly active antiretroviral therapy) and/or the infant during the lactation period, with early weaning by age 6 months, will reduce transmission through breast milk.