HIV SEXUAL TRANSMISSION RISK: ASSESSING THE EFFECTS OF COMBINING PREVENTION STRATEGIES

Purpose : The number of efficacious strategies available to prevent sexual transmission of HIV has increased following encouraging results of trials evaluating the effects of antiretroviral therapy (ART), preexposure prophylaxis (PrEP), and male circumcision.  HIV-discordant couples need guidance on the comparative effects of these and existing strategies alone, and in combination, on HIV transmission.

Methods: We estimated the sexual risk of HIV transmission over 1- and 10-year periods among male-male and male-female serodiscordant couples. We assumed the following reductions in transmission: 80% from consistent condom use; 54% from circumcision in the negative male partner of a heterosexual couple; 73% from circumcision in the negative partner of a male-male couple; 71% from PrEP in heterosexual couples; 44% from PrEP in male-male couples; and 96% from consistent ART use by the HIV-infected partner. The effects of insertive and receptive anal sex were also modeled.  In sensitivity analysis, we varied the number of sex acts, and the effects of ART, circumcision, condom use, and PrEP.

Results:   For couples using any single prevention strategy, a substantial cumulative risk of HIV transmission remained. For a male-female couple using only condoms, estimated risk over 10 years was 11%. For a male-male couple using only condoms, estimated risk was 76%. ART use by the HIV-infected partner was the most effective single strategy in reducing risk; among male-male couples, adding consistent condom use was necessary to keep the 10-year risk below 10% (Table 1). Of the parameters explored in sensitivity analysis, varying the number of monthly sex acts had the largest effect on the probability of HIV transmission. Increasing the efficacy of PrEP, per higher adherence, decreased the 1-year probability of HIV transmission among male-male couples from 34% to 6%.

Conclusions: Long-term transmission probabilities within serodiscordant couples can be high, though these can be substantially reduced with the strategic use of preventive methods, especially those that include ART.  Focusing on 1-year and longer-term transmission probabilities give couples a better understanding of risk than those illustrated by data for a single sexual act.