Antiretroviral Therapy (ART) as an HIV Prevention Strategy
Antiretroviral therapy (ART) has substantially improved the health and survival of people living with HIV worldwide. The primary benefit of ART to the HIV-infected individual comes from suppression of the viral load, which allows partial recovery of the immune system and prevents further immune compromise. Effective suppression of the viral load with ART may also decrease a person’s infectiousness and could conceivably curb the spread of HIV. Increasing ART use with the aim of decreasing HIV transmission is a potential prevention strategy in part because the primary tool, ART, is already available. The potential to benefit both the HIV-infected individual and the general population is an appealing aspect of this strategy.
Several studies and lines of reasoning support the potential of ART to decrease HIV transmission, but no direct evidence demonstrating this is yet available. First, HIV-infected individuals with lower viral loads are less likely to transmit HIV to their sexual partners. In one study in Uganda, no heterosexual transmissions occurred from HIV-infected persons with viral loads lower than 1700 copies/mL. Second, ART suppresses HIV RNA levels in the semen, vaginal secretions, and the rectum, which would logically be expected to decrease the risk of sexual transmission from those compartments. Finally, retrospective studies have demonstrated that patients on ART are less likely to have infected sexual partners.
The utility of widespread ART to decrease HIV transmission may be limited by several factors. Perhaps most importantly, only people who know they have HIV infection can be treated with ART. A substantial portion, in some countries the majority, of HIV-infected people do not know their status. Many are diagnosed at late stages of disease, when the opportunity to use ART to prevent transmission likely has passed. Additionally, most individuals do not start ART during acute infection, when it is hypothesized that a large proportion of forward transmission occurs. For these reasons, testing programs must improve in parallel with scale-up of ART programs. If patients increase risky sexual behavior after starting ART because they believe they are no longer able to transmit HIV, the prevention effect of ART could be negated. Furthermore, individuals on ART are more likely to be sexually active for longer periods of time given their improved health; increasing the length of time partners can be exposed to the virus. Increased use of and sub-optimal adherence to ART could lead to increased viral resistance. Moreover, the up-front cost of expanding and sustaining ART programs is likely to be substantial.
An ongoing, international, randomized controlled trial is testing whether ART can decrease the risk of transmitting HIV within serodiscordant heterosexual couples. That study is scheduled to be completed in 2011. Until the results of that trial are available, the studies summarized below provide the best sense of the prevention potential and limits of using ART to decrease HIV transmission.
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