A focus on stable couples when attempting to reduce HIV transmission through offering antiretroviral treatment, or when counselling about HIV transmission and safer sex, may risk understimating the amount of HIV infections that occur as a result of sex outside the primary relationship, according to results from a modelling study which looked at heterosexual couples in sub-Saharan Africa.
“Extra-couple transmission has played and still plays a major part in driving HIV incidence for both sexes,” write the authors in an advance online publication in The Lancet. They believe that HIV prevention strategies, including those based on treatment-as-prevention approaches, will not be sufficient to control the continued spread of HIV if they only focus on couples where one partner is HIV positive and the other HIV negative (serodiscordant relationships).
“Our results do imply that behavioural and biomedical interventions focused on serodiscordant couples will not be sufficient to cause major reductions in HIV incidence at a population level,” comment the investigators. “Policy choices should be made in view of our finding that extra-couple transmission by both sexes has a major role in the HIV epidemic in sub-Saharan Africa.”
Antiretroviral therapy has the potential to make a major impact on the HIV epidemic. Results of a large study involving serodiscordant heterosexual couples showed that HIV treatment that suppresses viral load to undetectable levels reduces the risk of transmission by 96%. Pre-exposure prophylaxis (PrEP) study results are also promising.
There is now a debate about how best to use antiretroviral therapy to reduce HIV incidence. One possible approach is to target serodiscordant couples. Another is the so-called test-and-treat strategy, which consists of the annual HIV testing of the sexually active population and immediate antiretroviral therapy for those testing positive.
Some research has suggested that large numbers of HIV infections in sub-Saharan Africa occur outside the context of steady relationships. Investigators used data gathered in surveys conducted between 2003 and 2011 in 14 sub-Saharan African countries involving 27,000 cohabiting heterosexual people to model the dynamics of HIV transmissions. They wished to establish the proportion of infections that occurred before relationship formation; within relationships; and because of sex outside relationships.
Their model took into account factors such as relationship duration, age at sexual debut, individual HIV infection status, country-wide HIV prevalence and coverage of antiretroviral therapy.
Overall, the investigators calculated that 30% of all new HIV infections in men and 10% in women within stable relationships were due to sex outside the relationship.
In serodiscordant couples, between 50 and 80% of infections in men and 31 and 74% in women were estimated to be due to extra-couple intercourse. In couples where both partners were HIV positive, 18 to 51% of infections in men and 13 to 29% in women were thought to have a similar source.
Their estimates for 2011 showed that between 0.22 and 13% of new infections among men and 0.094 and 6.2% of incident infections among women in serodiscordant relationships were likely to have an extra-couple source.
The authors highlight molecular evidence showing the importance of extra-couple transmission. “In several cohort studies of serodiscordant couples, 13-32% of incident infections were from virus not linked to that isolated from the seroconverter’s partner and were presumably due to extra-couple intercourse.”
They believe their findings have implications for the use of HIV treatment as prevention. “Interventions should address all transmission routes to fight the epidemic. Despite its expense and logistical demands, the universal test-and-treat strategy could reduce all forms of heterosexual transmission.”
Bellan SE et al. Extra-couple HIV transmission in sub-Saharan Africa: a mathematical modelling study of survey data. The Lancet, online edition, Dx.doi.org/10.1016/s0140-6736(12)61960-6, 2013.