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Introduction: The recent availability of efficacious prevention interventions among stable couples offers new opportunities for reducing HIV incidence in sub-Saharan Africa. Understanding the dynamics of HIV incidence among stable couples is critical to inform HIV prevention strategy across sub-Saharan Africa., Methods: We quantified the sources of HIV incidence arising among stable couples in sub-Saharan Africa using a cohort-type mathematical model parameterized by nationally representative data. Uncertainty and sensitivity analyses were incorporated., Results: HIV incidence arising among stable concordant HIV-negative couples contribute each year, on average, 29.4% of total HIV incidence; of those, 22.5% (range: 11.1%-39.8%) are infections acquired by one of the partners from sources external to the couple, less than 1% are infections acquired by both partners from external sources within a year and 6.8% (range: 3.6%-11.6%) are transmissions to the uninfected partner in the couple in less than a year after the other partner acquired the infection from an external source. The mean contribution of stable HIV sero-discordant couples to total HIV incidence is 30.4%, with most of those, 29.7% (range: 9.1%-47.9%), being due to HIV transmissions from the infected to the uninfected partner within the couple. The remaining incidence, 40.2% (range: 23.7%-64.6%), occurs among persons not in stable couples., Conclusions: Close to two-thirds of total HIV incidence in sub-Saharan Africa occur among stable couples; however, only half of this incidence is attributed to HIV transmissions from the infected to the uninfected partner in the couple. The remaining incidence is acquired through extra-partner sex. Substantial reductions in HIV incidence can be achieved only through a prevention approach that targets all modes of HIV exposure among stable couples and among individuals not in stable couples.

Objective: To estimate the contribution of HIV-1 sero-conversions among stable HIV sero-discordant couples (SDCs) to total HIV population-level incidence in sub-Saharan Africa., Design and Methods: We constructed a mathematical model, grounded in nationally representative demographic and epidemiological data, that estimates the annual number of HIV-1 transmissions from the infected partners to the uninfected partners among established SDCs, and compares its value to an estimate for the overall HIV population-level incidence in 20 countries in sub-Saharan Africa. We defined identifiable HIV-1 transmissions among SDCs as those that a hypothetical screening and intervention program would have the potential to avert. Uncertainty and sensitivity analyses were incorporated to assess the robustness of the findings., Results: Across the 20 countries, an average of 29% (range: 10-52%) of new HIV-1 infections occurred in which one partner in an identifiable SDC infected the other. The percentage of total HIV new infections in a country that occurred within such identifiable SDCs tended to be lower in countries with larger general population HIV epidemics. For most countries, HIV-1 incidence among SDCs is unlikely to exceed 50% of new HIV infections in the whole population., Conclusion: Only a fraction of HIV-1 heterosexual transmissions occur within identifiable SDCs. Prevention within SDCs at scale requires a series of potentially challenging programmatic requirements to be met. Despite the importance of prevention programs aiming at protecting the sero-negative partner in an SDC, a wider strategy utilizing the full range of prevention modalities, which would limit the original generation of SDCs, is also needed.

Two letters to the editor are presented in response to the article "A Tale of Two-Component Generalised HIV Epidemics," by James Shelton published in the March 20, 2010 issue, including a comment and the author's reply.