Combination prevention: the key to effective long term HIV prevention in serodiscordant couples

HIV sexual transmission risk among serodiscordant couples: assessing the effects of combining prevention strategies.

Lasry A, Sansom SL, Wolitski RJ, Green TA, Borkowf CB, Patel P, Mermin J. AIDS. 2014 Jun 19;28(10):1521-9. doi: 10.1097/QAD.0000000000000307.

Background: The number of strategies to prevent HIV transmission has increased following trials evaluating antiretroviral therapy (ART), pre-exposure prophylaxis (PrEP) and male circumcision. Serodiscordant couples need guidance on the effects of these strategies alone, and in combination with each other, on HIV transmission.

Methods: We estimated the sexual risk of HIV transmission over 1-year 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 ART use by the HIV-infected partner.

Findings: 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%.

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

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Editor’s notes: This mathematical modelling study by Lasry et al, seeks to estimate how existing prevention strategies might be used by serodiscordant couples in hetero- and homosexual relationships to obtain optimal reduction in risk of HIV transmission. They illustrate that even modest transmission probabilities for a given type of sex act can accumulate into substantial risk over time. While it is recognised that anal sex poses a high risk for HIV transmission, the projections in this study show the extent of accumulated risk. The study importantly shows that condom use alone, provides quite inadequate protection over time. Not surprisingly given recent evidence, antiretroviral therapy (ART) had the most substantial protective effect. But condom use is an important adjunct to minimise long-term transmission risk. This is not only, but especially with consistent anal sex as in male homosexual, serodiscordant couples. The most important take-home finding of this study in influencing prevention messaging, is its quantitative illustration that combination prevention is the key to effective HIV prevention. 

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