Estimating the proportion of new HIV infections that occur within married/cohabiting couples in urban Zambia and Rwanda

Background: Marriage is increasingly recognized as a potentially high-risk setting for heterosexual HIV transmission, especially for women, but few attempts have been made to estimate the burden of HIV attributable to marital transmission and HIV prevention efforts remain focused on abstinence and non-marital sex.

Methods: We used population-based Demographic and Health Survey data on sexual behaviour and service-based data on HIV serodiscordance among couples in urban Zambia and Rwanda to estimate the proportion of annually incident heterosexual HIV transmission which takes place within married or cohabiting couples in these settings.

Results: Under our base model, we estimate that 55.7% to 92.8% of new heterosexually acquired HIV infections among sexually active adults in urban Zambia and Rwanda occur within serodiscordant marital/cohabiting relationships, depending on sex of the index partner and location. Under our extended model, which considers the higher rates of reported condom use with non-cohabiting partners, we estimate that 60.7% to 94.3% of new heterosexually acquired HIV infections among sexually active adults in these settings occur within heterosexual serodiscordant marital/cohabiting relationships. We estimate that a couples-based intervention which reduced transmission in serodiscordant urban cohabiting couples to 7% per annum could avert 36.1% to 60.3% of HIV infections that would otherwise occur.

Conclusion: The majority of heterosexual HIV transmission for both men and women in urban Zambia and Rwanda takes place within marriage or cohabitation. We therefore call for increased promotion of couples-based voluntary counselling and testing and for development of other evidence-based, culturally and gender-sensitive interventions targeting heterosexual couples.