The current study sought to assess trends in South Africa's HIV incidence and determine the extent to which prevention and treatment programs have reduced that incidence.

The researchers adapted two models of the South African HIV epidemic -- the STI-HIV Interaction model and the ASSA2003 AIDS and Demographic model. A Bayesian approach was used to fit both models to age-specific HIV prevalence data from antenatal clinic surveys and household surveys.

Both models suggest that HIV incidence in people ages 15-49 declined significantly from the beginning of 2000 to the start of 2008: by 27 percent (95 percent confidence interval: 21 percent-32 percent) in the STI-HIV model and by 31 percent (95 percent CI: 23 percent-39 percent) in the ASSA2003 model, when expressed as a percentage of incidence rates in 2000.

By 2008, the percentage reduction in incidence owing to increased condom use was 37 percent (95 percent CI: 34 percent-41 percent) in the STI-HIV model and 23 percent (95 percent CI: 14 percent-34 percent) in the ASSA2003 model.

"Both models also estimated a small reduction in incidence due to antiretroviral treatment by 2008. Increased condom use therefore appears to be the most significant factor explaining the recent South African HIV incidence decline," the researchers concluded.

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