One study of the effectiveness of ART in reducing heterosexual transmission of HIV involved analysis of 393 serodiscordant heterosexual couples from 1991-2003. The authors noted that heterosexual transmission was reduced by 80% when the positive partner was treated with ART. Despite this significant reduction, the investigators cautioned against continued possible risk of transmission because of HIV levels in genital secretions of patients on ART [1]. Among 193 discordant couples identified in the Rakai Cohort in which the infected partner had a CD4 counts under 250 cells/µL, no transmission events were observed among 20 couples in which the infected partner was on ART [3]. A study of 2993 discordant couples in Rwanda and Zambia demonstrated that ART use was associated with reduced (but not eliminated) rates of HIV transmission and reduction in unprotected sex [4].
Regarding potential reduction of risk within MSM populations, analysis of data from the San Francisco Young Men's Health Study evaluated transmission events among 534 MSM. The investigators found a 60% decrease in HIV transmission after the introduction of ART. The reduction occurred despite the increases in reported number of risky sexual behaviors [5].
Other information regarding the potential population-level benefit of ART on transmission comes from mathematical modeling studies. Mathematical models involve the development of equations to explain the relationship between the potential effects of ART on viral load and the likelihood of HIV transmission. Modeling can help predict population-level outcomes such as rate of drug resistance, rate of HIV infection or prevalence of infection, and effects of HIV treatment and prevention programs in various settings [33]. Modeling methods are useful tools, but are limited by the fact that models reflect current understanding of how HIV is transmitted [34], as well as the validity of the assumptions and data used in model construction.
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