An expert who was not involved in the study said it suggests the possibility of virtually eliminating mother-to-child HIV transmission in the United States, an idea that would have been almost unimaginable a few years ago.
"This is a remarkable success story for ... everybody involved in caring for these women and the women themselves," said the study's lead author, Dr. Mary Lou Lindegren, a medical epidemiologist with the Centers for Disease Control and Prevention in Atlanta.
"We still have more to go, but we've been dramatically successful," she said.
The number of babies who developed AIDS after being infected with HIV before or during birth peaked at 907 in 1992 and then declined 67 percent over the next five years, to 297 in 1997, the researchers reported in the Journal of the American Medical Association.
Researchers analyzed AIDS reports from all 50 states and detailed HIV data on mothers and children in the 18 states that collected HIV information.
Researchers believe far more babies were born HIV-infected than actual AIDS reports reveal, since it can take years for HIV to develop into AIDS. The CDC estimates that 1,650 babies caught HIV from their mothers in 1991, at the epidemic's peak. By 1996, that number had fallen to 480, a 71 percent drop, Lindegren said.
Scientists discovered in 1994 that treatment with AZT, now called zidovudine, reduced the newborn's risk of catching HIV from 26 percent to 8 percent. The drug was given to HIV-infected women during pregnancy and labor and to the newborn for the first six weeks of life, said Dr. Lynne M. Mofenson of the National Institute of Child Health and Human Development.
In actual practice, the protection can be even greater, lowering risk to as low as 3 percent, Mofenson noted in an editorial accompanying the study, citing other research. Delivering at-risk babies by Caesarean section lowers it further, she noted.
Also, if women are getting treatment with powerful new AIDS-fighting drug regimens that can reduce virus levels in the blood to smaller-than-detectable amounts, the risk may fall to less than 1 percent, she said, again citing other research.
Virtual elimination of mother-to-child transmission in the U.S. looks possible, Mofenson said.
Authors of the new study said zidovudine isn't the only reason for the drop in AIDS cases among children who caught HIV during birth in recent years. For example, the overall number of babies born to infected women fell 17 percent during the study period. But such factors cannot explain the striking reduction since late 1994 in the number of babies that develop AIDS; the main reason was clearly prenatal zidovudine, they said.