Effect of Antiretroviral Therapy on Risk of Sexual Transmission of HIV Infection and Superinfection

Effect of Antiretroviral Therapy on Risk of Sexual Transmission of HIV Infection and Superinfection

Background

The past decade has seen substantial advances in the development of antiretroviral therapy (ART)—medications used in combination to reduce the replication of HIV virus and treat HIV-infected persons. Because of these medications, many HIV-infected persons are able to reduce levels of virus in the bloodstream (plasma viral load) to undetectable levels. Data suggest that HIV-infected persons with undetectable viral load are less infectious, and may be less likely to transmit HIV via sexual contact. This fact sheet summarizes the implications of these data to individual couples and to the potential impact of ART in the prevention of HIV transmission within populations.

Prevention of Sexual Transmission of HIV: Individual Couples vs. Populations

Evidence from observational studies among heterosexual populations [1-4] and men who have sex with men (MSM) [5] suggests that effective ART may greatly reduce the likelihood of sexual transmission from infected individuals to their sexual partners. A study of heterosexual couples in Uganda in which one partner was infected revealed that infected persons who did transmit virus to their partners had significantly higher mean viral load than those who did not transmit (90,254 copies/mL vs. 38,029 copies/mL); no transmissions occurred among couples in which the infected partners viral load was under 1500 copies/mL [1]. Among infected persons at a clinic in Spain , wider availability of effective ART was associated with an 80% decrease in sexual transmission of HIV [2]. While fewer data are available regarding the impact of ART on transmission among MSM (the most affected population in the United States ), transmission rates observed among a population of MSM in San Francisco declined with the availability of ART despite increases in risk behavior, associated with an estimated 60% decrease in per-act infectivity [5]. Mathematical modeling studies suggest that successful use of ART by enough infected individuals could substantially reduce the spread of HIV within a population [6-7]. ART thus holds promise as an important prevention tool. However, it is important to note that this potential reduction in HIV transmission within a population does not translate to elimination of transmission risk within individual couples.