HIV patients on antiretroviral therapy are less likely to transmit the virus to their seronegative partners, according to new research presented Wednesday in San Francisco at the 17th Conference on Retroviruses and Opportunistic Infections. The news could boost efforts to provide ARVs for patients in developing countries, and it adds to the debate over how billions of dollars are spent on global HIV treatment and prevention programs.

Dr. Deborah Donnell, affiliated with the Fred Hutchinson Cancer Research Center in Seattle, and colleagues closely followed 3,400 serodiscordant couples in seven African countries for the study. All couples were counseled on prevention and given free condoms. The HIV-infected partners were put on ARVs when their immune system CD4 cell counts reached a predefined level.

Over the next three years, 103 previously uninfected partners seroconverted. Of those transmissions, 102 occurred before the HIV-positive partner had been placed on ARVs, Donnell said.

"Only one happened when the partner was on antiretroviral therapy," said Donnell. "That amounts to a final reduction of 92 percent when on antiretroviral therapy."

The couples were tested every few months, and researchers could determine whether the partner who seroconverted acquired the virus from someone outside of the primary partnership.

"We think it is very likely that antiretroviral treatment is