HIV transmission: Does anti-retroviral therapy reduce risk?

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HIV transmission: Does anti-retroviral therapy reduce risk?

Question

Can anti-retroviral therapy reduce the risk of HIV transmission to sexual partners?

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Answer

A growing body of evidence suggests that it can. Several studies of trends in HIV infection and treatment within defined populations have shown that the number of new cases of HIV falls as HIV treatment — called anti-retroviral therapy (ART) — becomes more common. These studies, however, fall short of proving that ART is the variable responsible for reducing rates of HIV transmission.

Now a large controlled study of nearly 1800 couples in which one partner is HIV positive and the other is not (serodiscordant couples) may provide the missing link.

Study participants were randomly assigned to two groups. In the first group, the HIV-infected partner began taking ART regardless of the amount of damage his or her immune system had sustained, as measured by the level of CD4 cells. These CD4 cells, a subset of white blood cells, also known as T cells, are the body's first defense against foreign invaders and one of the main targets of HIV. In the second group, the HIV-infected partner did not start ART until the CD4 cell count was too low to fight off AIDS-related infections, or until another marker of advanced immune deficiency developed.  All the couples in the study were counseled to keep using condoms and following other safe sex practices.

The study was terminated earlier than planned because interim results indicated that HIV-negative men and women in the first group, whose partners received ART immediately, were 96 percent less likely to become infected than were those with partners who were not treated until their immune systems were failing.

HIV spreads in the body by hijacking CD4 cells and using their DNA to make copies of itself (replicate). In the process, it destroys CD4 cells. Anti-retroviral drugs are designed to halt the replication process and preserve the immune system. Because different types of anti-retroviral drugs attack the virus at different stages of replication, ART combines three or more drugs, a strategy that increases the chances of stopping the progression of the disease. The goal is to lower the amount of virus in the blood (viral load) to the point where it is virtually undetectable in the bloodstream.

The encouraging results don't mean that HIV treatment eliminates the risk of HIV transmission in serodiscordant couples. Questions remain about whether viral load is an adequate indicator of risk of sexual transmission. Similarly, researchers don't know how closely viral load is correlated with the amount of virus in other body fluids, including semen. Finally, this study looked primarily at heterosexual couples (97 percent of participants); more research is needed, especially in men who have sex with men.

Last Updated: 2011-07-14
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