With the massive amounts of HIV infecting women throughout the developing world, "safe" breastfeeding is fast becoming an important issue. In general (but particularly in the developing world), breast feeding is crucial in that it has been shown to directly lower rates of malnourishment in infants/young kids as well as decrease rates of infectious diseases (in young kids). Thus, it is important that young infants have access to the benefits of breast milk...without the risk of contracting HIV.
Despite efforts to give pregnant women antiretrovirals prior to labor and during labor as well as giving the antiretrovirals to the baby being born have helped decrease the amount of kids that will acquire HIV infection during the birthing process. However, a problem still exists in that many kids that are born uninfected are becoming infected by contaminated breast milk. In fact, breast feeding is responsible for nearly half (48%). Since breast milk may be the only form of nutrients available to young infants in developing nations (for many reasons including limited access to sanitized water to mix in with formula, limited finances, cultural taboos, etc.), it may be too steep a tradeoff to risk stopping breast feeding practices to prevent potential HIV infection (if knowledge of having HIV is even available).
Researchers have recently found that extending the use of antiretrovirals in infants and breast feeding mothers for a longer amount of time (up to 6 months) can DRASTICALLY reduce the incidence of post-natal transmission of HIV. Specifically in a study in Malawi, out of the infants who were given antiretrovirals (Nevirapine) for the first 10 weeks of life, only 3.1% became infected from contaminated breast milk...compared with the control group which only received one dose of nevirapine and one week's worth of AZT which experienced 10% infection with HIV.
How it is ethical to have a control group in an HIV treatment study, I am not sure.