HIV poses hazards for breast feeding.

A study conducted in Africa adds to evidence implicating breast milk as the culprit in some cases of mother-to-child transmission of HIV, the virus that causes AIDS.

Previous studies have shown a 10 to 60 percent chance that an infected mother will pass HIV to her unborn fetus. If the fetus escapes that in utero threat, it may acquire the infection during delivery. In addition, several case reports suggest that HIV-tainted breast milk may, at times, infect newborns.

Now, in the largest study of mother-to-child HIV transmission to date, Philippe Van de Perre at the AIDS Reference Laboratory in Kigali, Rwanda, demonstrates that women who test negative for the AIDS virus at the time of delivery, but who become infected, can later pass the virus on to their infants, probably via breast feeding.

Van de Perre and an international team of AIDS experts studied 212 pregnant women who tested negative for HIV when they delivered. Within three to 18 months later, 16 of these women tested positive for HIV, the team reports in the Aug. 29 NEW ENGLAND JOURNAL OF MEDICINE.

At some point during the 18-month period, nine of the 15 infants tested positive for HIV, either with an antibody test or with a method called polymerase chain reaction, which detects the virus itself.

The researchers believe one child acquired the infection in utero because it tested positive for HIV at birth. Another four infants, who tested negative at birth, showed signs of infection during the first three months of life. That time frame suggests HIV exposure in the womb or at delivery, says Philip A. Pizzo of the National Cancer Institute. Previous studies have suggested that infected newborns may initially test negative, and then test positive within three months after birth.

In four other cases, however, the study implicates breast feeding as the route of HIV transmission, Pizzo notes. These infants, who tested negative at birth, developed their infections at four to 21 months later -- all within three months of their mothers' positive HIV tests.

If they had acquired the infection in the womb or during birth, these infants probably would have detectable amounts of HIV in their blood much earlier, Pizzo says. Thus, he says, the study affirms that "breast feeding can be a source of transmission."

Should at-risk mothers avoid breast feeding, even though they show no sign of HIV? In developing countries, notes Pizzo, breast feeding is complicated by the threat of unsafe water, which could lead to life-threatening diarrhea in bottle-fed infants. But in the United States, bottle feeding remains the safe alternative both for HIV-infected mothers and for those worried about their HIV status, asserts Peter Vink at the University of Maryland School of Medicine in Baltimore.

-- K. A. Fackelmann