A decline in new HIV infections in South Africa: estimating HIV incidence from three national HIV surveys in 2002, 2005 and 2008

Abstract

Background: Three national HIV household surveys were conducted in South Africa, in 2002, 2005 and 2008. A novelty of the 2008 survey was the addition of serological testing to ascertain antiretroviral treatment (ART) use.

Methods and principal findings: We used a validated mathematical method to estimate the rate of new HIV infections (HIV incidence) in South Africa using nationally representative HIV prevalence data collected in 2002, 2005 and 2008. The observed HIV prevalence levels in 2008 were adjusted for the effect of antiretroviral treatment on survival. The estimated "excess" HIV prevalence due to ART in 2008 was highest among women 25 years and older and among men 30 years and older. In the period 2002-2005, the HIV incidence rate among men and women aged 15-49 years was estimated to be 2.0 new infections each year per 100 susceptible individuals (/100pyar) (uncertainty range: 1.2-3.0/100pyar). The highest incidence rate was among 15-24 year-old women, at 5.5/100pyar (4.5-6.5). In the period 2005-2008, incidence among men and women aged 15-49 was estimated to be 1.3/100 (0.6-2.5/100pyar), although the change from 2002-2005 was not statistically significant. However, the incidence rate among young women aged 15-24 declined by 60% in the same period, to 2.2/100pyar, and this change was statistically significant. There is evidence from the surveys of significant increases in condom use and awareness of HIV status, especially among youth.

Conclusions: Our analysis demonstrates how serial measures of HIV prevalence obtained in population-based surveys can be used to estimate national HIV incidence rates. We also show the need to determine the impact of ART on observed HIV prevalence levels. The estimation of HIV incidence and ART exposure is crucial to disentangle the concurrent impact of prevention and treatment programs on HIV prevalence.

Figure 1. HIV prevalence in South Africa in (a) 2002, (b) 2005 and (c) 2008.

The dark bars show the prevalence among men and the lighter bars show the prevalence among women. Source: Human Science Research Council Surveys .

Figure 2. The impact of antiretroviral therapy on HIV prevalence in 2008 for (a) men and (b) women.

In each panel, the overall height of the bars shows HIV prevalence; the white part shows those HIV-infected but not on treatment; the grey part shows those on treatment but who would be still alive without treatment; and, the red part shows those on treatment who are alive due to treatment. The estimate of the proportion alive due to treatment is based on assumptions that treatment is initiated one year before when individuals would otherwise die, and that individuals on treatment suffer a 10% annual mortality rate in first years of treatment.

Figure 3. Estimates of HIV incidence rate in South Africa, 2002–2005 (light grey bars) and 2005–2008 (dark red bars), using cross-sectional HIV prevalence data collected in 2002, 2005 and 2008.

The error bars for the 2002–2005 estimates show the 95% uncertainty interval due to measurement errors in the prevalence data; the error bars for the 2005–2008 estimates show the uncertainty due to measurement error and the use of alternate assumptions for the ART adjustment (described in the text).

Figure 4. Key behavioural indicators among women aged 15–24 year in the 2002, 2005 and 2008 surveys.

Indicators are: fraction reporting two or more partnerships in the last 12 months, fraction reporting condom use at last sex, and fraction that reported having an HIV test in the last 12 months. The question on testing in the last 12 months was not asked in 2002.