Antiretrovirals and condoms will have more effect on HIV in South Africa than circumcision, model finds

Gus Cairns, Michael Carter
Published: 23 July 2009

In preliminary results from a mathematical model set up by researchers from the British Columbia Centre for Excellence in HIV/AIDS, male circumcision was found to have a considerably lower impact than condom use or antiretorviral therapy (ART) coverage on new HIV infection rates and on death rates in men in South Africa.

Researchers seeking to assess the population-level impact of different HIV prevention strategies in South Africa have developed a mathematical model that identifies increased condom use and ART coverage as keys to reducing new HIV infections in that country. Using published data from 2003 to 2008 for calibration, the model compared simulated scenarios involving various levels of male circumcision, condom use and ART coverage up to 2025.

The simulations set male circumcision rates at 51% (current level), 75% and 90%; condom use rates at 14% (current level), 50%, 75%, 80% and 90%; and ART coverage at 21% (current level), 50%, 75%, 80% and 90% with a CD4 cell count of 200 cells/mm3 or lower as the primary criterion for initiating ART.

Condom efficacy with 100% use was set at 90% and the efficacy of circumcision in preventing new infections at 53%. The infectiousness of HIV-positive members of the population was set in six strata: primary infection (less than 12 weeks after infection); chronic infection with viral load under 1000; viral load between 1000 and 10,000; viral load from 10,000 to 100,000; viral load over 100,000; and late-stage disease.

Other assumptions in the current model included that 50% of infected people knew their serostatus and, for the purposes of this initial, simple version of the model, that the both the number of women infected with HIV and their infectiousness would remain the same; obviously in a more sophisticated model which includes both male and female infections, reductions in female infections and infectiousness would have a synergistic effect. The impact of ART, condoms and circumcision in women is currently being calculated.

Impacts on the heterosexual male population aged 15 to 49 were measured.

Presenter Viviane Lima told the conference that scaling condom use up from 14% (the current estimated level) to 50% and antiretroviral therapy coverage from 21% to 80% would result in an estimated 950,000 infections averted in men by 2019. Raising ART use to 50% and condom use to 80% would have a similar effect.

Raising both to 50% would result in 700,000 fewer infections. But raising circumcision rates from the current 51% of men circumcised to 90% would only add another 48,000 infections averted to this total.

Condom use and ART coverage, alone or in combination, were found to reduce new HIV infections by from 64% to 95% by 2025 and to reduce mortality by 10% to 34%. Circumcision brought about a 3% to 13% reduction in new HIV infections and a 2% to 4% reduction in mortality; according to Lima, its impact “was overshadowed when combined with the other interventions.

“We were surprised by how little effect it had,” she said.

The mathematical model is susceptible of a huge number of permutations. Forthcoming studies include testing the effect of different numbers of people coming forward for testing, drug resistance, different criteria for starting treatment, mother to child transmission, and many other variables.

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