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We've long believed that treating HIV-infected individuals will reduce the likelihood of their transmitting the virus to others — but does this actually hold true for heterosexual transmission as it does for vertical transmission? The jury's still out, but results presented at CROI this year from an observational cohort study of serodiscordant couples in Rwanda and Zambia point in a positive direction (JW AIDS Clin Care Mar 9 2009).
In that study, the rate of new infections was 3.4 per 100 person-years when infected partners were not taking antiretroviral therapy (ART), versus 0.7 per 100 person-years when they were taking ART. Notably, unprotected sex was less common when infected partners were on ART than when they were not, suggesting that ART and prevention counseling were working synergistically to reduce the risk for transmission.
A mathematical model using population-level data from South Africa suggests that ART could also reduce heterosexual transmission on a broader scale — and that the HIV epidemic could be all but eliminated if universal testing and immediate treatment were implemented (JW AIDS Clin Care Dec 15 2008).
These and other studies led the U.S. Department of Health and Human Services to state in their latest treatment guidelines that the use of effective ART, regardless of CD4-cell count, is likely to reduce transmission to uninfected sexual partners (evidence level, BII). However, definitive answers require a randomized trial such as the ongoing HPTN 052 study and will not be available for some time. What should we as clinicians do in the meantime?
Prescribe ART to HIV-infected individuals who are in a serodiscordant relationship, regardless of their CD4-cell count, so as to decrease the risk of transmission to the uninfected partner.
Continue to remind patients that even with an undetectable viral load, the risk of transmission is probably not zero.
Continue to counsel patients on safer sex, as any biological reduction in infectivity gained with ART use could be offset rapidly by an increase in risky behavior.