ArticlesNew heterosexually transmitted HIV infections in married or cohabiting couples in urban Zambia and Rwanda: an analysis of survey and clinical data
Introduction
Evidence suggests that a woman's greatest risk of contracting HIV lies within a marital relationship.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 Fewer attempts have been made to understand a man's risk within marriage;2, 12 but, in regions with generalised epidemics, high rates of serodiscordance among heterosexual couples in which the woman is HIV-positive suggest that a man's risk of marital HIV acquisition could also be substantial.2, 12, 13
Sub-Saharan Africa has the highest prevalence and incidence of HIV infection worldwide, mostly attributable to heterosexual transmission.14 Various studies have noted a high prevalence of HIV serodiscordance among heterosexual couples in Africa;15, 16, 17 population-based estimates of serodiscordance, from Demographic and Health Surveys (DHS), range from 2% (in Rwanda)13 to 13% (in Zimbabwe18 and Lesotho19). DHS data which show that between 45%18 and 75%20 of married HIV-positive individuals have HIV-negative spouses affirm the importance of HIV-prevention efforts for couples.18 Studies in Rwanda and Zambia with serodiscordant heterosexual couples showed that HIV transmission from HIV-positive to HIV-negative partners was 20–25% per year, irrespective of whether the man or woman was the positive partner.21, 22, 23 This rate accords with a coital frequency of two to three times per week and a risk of transmission on the order of one in 500 for each contact.23, 24, 25 Transmission in serodiscordant couples who have received joint voluntary counselling and testing ranges from 3% to 7% per year,21, 26, 27 with higher rates reported in cohorts that include a mixture of couples who know their own serostatus or that of their partner and those who don't.23, 25, 27 These data show that HIV-serodiscordant partnerships are a risky context for both women and men. These partnerships are also a potentially valuable context for preventive interventions.
We aimed to use both publicly available population-based data on sexual behaviour and service-based estimates of HIV serodiscordance to assess the proportion of heterosexually transmitted HIV infections in urban Zambia and urban Rwanda during a typical 12 month period which occur within the context of marital or cohabiting relationships. By quantifying the extent of HIV transmission among couples, we aimed to inform and perhaps to redirect the focus of HIV-intervention efforts, which have traditionally targeted individuals rather than couples.
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Data sources
We used data collected by the Rwanda–Zambia HIV Research Group from July, 2003, to December, 2005, through voluntary counselling and testing services for couples in Kigali, Rwanda, and Lusaka, Zambia. Both partners were present at counselling sessions both before and after HIV tests, with simultaneous disclosure of results, results-specific counselling, training in the use of condoms, and referrals as appropriate for follow-up care.29 Data were available from 15 159 cohabiting couples and 8690
Results
In the DHS data for urban Zambia, 1739 (68·2%) women and 540 (78·4%) men reported sexual activity in the past 12 months, whereas in urban Rwanda, 1176 (45·0%) women and 606 (53·6%) men reported sexual activity in the past year (figure). The difference in sexual activity in the two areas is probably associated with the older average age of first sexual intercourse in Rwanda.13, 30, 31
Overall, 1388 (79·8%) of the sexually active Zambian women, 345 (63·9%) of the Zambian men, 997 (84·8%) of
Discussion
HIV prevalence in urban areas of Zambia in 2001 was 19·2% in men aged 15–59 and 26·3% in women aged 15–49.30 In 2005, urban HIV prevalence in Rwanda was 5·8% in men and 8·6% in women.13 Our most conservative model (model 1), predicted that most heterosexual HIV infections in both men and women in urban Zambia and Rwanda every year are probably transmitted within marriage. Our sensitivity analyses affirm the robustness of our key finding that most new heterosexually transmitted HIV infections in
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