Antiretroviral Therapy Reduces Heterosexual HIV Transmission Risk by More than 90%

HIV positive people on antiretroviral therapy (ART) were 92% less likely than untreated individuals to transmit the virus to their heterosexual partners, according to an African study reported in the May 27, 2010 advance online edition of The Lancet. Among untreated partners, greater transmission risk was associated with lower CD4 cell count and higher viral load. The researchers concluded that ART could be an effective strategy for achieving population-level reductions in HIV transmission.

A growing body of evidence indicates that use of antiretroviral drugs can dramatically reduce the risk of HIV transmission. This strategy is already widely employed to prevent mother-to-child HIV transmission, and ART may reduce sexual transmission in a population as well.

Deborah Donnell, Connie Celum, and fellow investigators with the Partners in Prevention HSV/HIV Transmission Study Team assessed the effect of ART on HIV transmission within serodiscordant heterosexual couples in 7 countries in southern and eastern Africa (Botswana, Kenya, Rwanda, South Africa, Tanzania, Uganda, and Zambia).

The Partners in Prevention trial -- a 6-year study funded by the Bill & Melinda Gates Foundation -- was designed to test whether treating herpes simplex virus (HSV) infection with acyclovir would reduce the rate of HIV transmission; as previously reported, it did not.

The researchers also performed a prospective analysis looking at the association between ART use and HIV infection. This analysis included 3381 couples in which one partner was positive for both HIV-1 and HSV-2 and the other partner was HIV negative.

At enrollment, all HIV positive participants had a CD4 cell count of 250 cells/mm3 or higher (median about 450 cells/mm3) and no history of AIDS-defining conditions, and therefore did not meet national guidelines for ART initiation in effect at the time. During a follow-up period of up to 24 months, CD4 counts were measured every 6 months, and participants started ART if their CD4 level fell below guidelines criteria (usually 200 cells/mm3).

Participants were counseled and advised to practice protected sex. Initially negative partners were tested for HIV every 3 months. If they were found to be infected, genetic sequencing was done to determine whether they had the same HIV strain as their partner, indicating that transmission probably occurred between the couple rather than from an outside partner.

Results

Based on these findings, the investigators concluded, "Low CD4 cell counts and high plasma HIV-1 concentrations might guide use of ART to achieve an HIV-1 prevention benefit." That is, people with more than 200 cells/mm3 might be advised to start treatment if they have high viral load.

The researchers added that, "Provision of ART to HIV-1 infected patients could be an effective strategy to achieve population-level reductions in HIV-1 transmission." They emphasized however -- as has been shown in other studies -- that while ART dramatically lowers the risk of HIV transmission, it is not eliminated entirely.

"[T]he one transmission indicated that HIV serodiscordant couples should maintain safer-sex practices even when HIV-positive partners are on treatment," Dr. Donnell said in a press release issued by the University of Washington.

In an accompanying editorial, Francois Dabis from Universite Victor Segalen and co-authors argued that there is now enough evidence to justify population-level trials of ART for HIV prevention.

"During the hour or so it takes to read this comment and linked article, 300 new HIV infections will have occurred in Africa," they wrote. "We should not wait for the results of further models, observational studies, or the ongoing couple-based prevention trial before engaging in population-based trials of 'test-and-treat'."

6/4/10

References

D Donnell, JM Baeten, J Kiarie, C Celum and others (Partners in Prevention HSV/HIV Transmission Study Team). Heterosexual HIV-1 transmission after initiation of antiretroviral therapy: a prospective cohort analysis. The Lancet. May 27, 2010 (Epub ahead of print).

F Dabis, M-L Newell, and Bernard Hirschel. HIV drugs for treatment, and for prevention (Editorial). The Lancet. May 27, 2010 (Epub ahead of print).

Other source

University of Washington. Study in The Lancet:  Antiretroviral Therapy Associated with 92% Decreased Risk of HIV Transmission among HIV-1 Discordant Couples in a Large Multinational Study. Press release. May 27, 2010.