HIV prevention: don’t just target serodiscordant couples

A large proportion of heterosexual HIV transmission in sub-Saharan Africa occurs among stable couples who have sexual partners outside of their relationship, shows research published in TheLancet.

The researchers say that prevention strategies that target serodiscordant couples - where one partner is HIV-positive but the other is not - are therefore unlikely to be sufficient to reverse the HIV epidemic.

"Because of the large contribution of extra-couple transmission (from outside partnerships) to new HIV infections, interventions should target the larger sexually active population and not just serodiscordant couples," said author Steve Bellan (University of Texas, Austin, USA) in a press statement.

"Pre-couple (prior to relationship), extra-couple, and within-couple transmission are all common, and HIV control policies that address all these routes are needed to stem the HIV epidemic in Africa."

The study used data from 27,201 cohabiting couples in 18 sub-Saharan countries between 2003 and 2011 to model the dynamics of HIV transmission.

Overall, the authors estimate that extra-couple transmission, from sexual partners outside of a stable relationship, is responsible for 30-65% of HIV incidence in men and 10-47% in women, depending on the country analyzed.

And, within serodiscordant couples, up to 80% of HIV infections in men and 74% of infections in women were accounted for by extra-couple transmission.

The report also highlights that transmission is more likely to occur from men to women than vice versa, and that women are at particularly high risk for infection in the period before entering into cohabitation.

Bellan and colleagues conclude that prevention strategies (eg, antiretroviral treatment as prevention and pre-exposure prophylaxis) which target HIV-positive individuals in stable, serodiscordant couples are a good starting point for HIV control but will not result in major declines in HIV incidence. They say the optimum approach is a universal test-and-treat strategy that would reduce all forms of heterosexual transmission.

In an accompanying comment, Connie Celum and Jared Baeten (University of Washington, Seattle, USA) agree that HIV prevention strategies need to better reflect the reality of sexual relationships.

"Relationships are not static - ie, partnerships dissolve, some temporarily, and new, sometimes concurrent, partnerships are established, often with partners of unknown HIV serostatus with whom condoms are rarely used and HIV risk can be substantial," they write.

"Strategies to deliver evidence-based combination prevention efficiently and effectively, targeted at high-risk populations and with high coverage for those at risk, will maximize this incredible opportunity in the history of the HIV epidemic."

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