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21 Jun 2010

A decline in new HIV infections in South Africa

Dimakatso Mokwena
Press Release

New findings indicate that HIV incidence is declining and that the impact of antiretroviral treatment is having an effect on the South African epidemic.

In South Africa, more people live with HIV and AIDS than anywhere else and the country is currently implementing the largest antiretroviral treatment (ART) programme in the world. It is therefore befitting that South Africa has embarked on a series of repeated national population-based HIV surveys to help in monitoring the response as a nation to the HIV/AIDS epidemic. Three national HIV household surveys, led by the Human Sciences Research Council (HSRC) have been conducted in South Africa: the first in 2002, followed by surveys in 2005 and 2008. These surveys collected data not only on the HIV status but also information on socio-demographic and behavioural determinants which greatly enhanced the analysis and interpretation of the observed trends in HIV prevalence and incidence (new infections).

In an article by Thomas Rehle, Timothy Hallett, Olive Shisana et al, published in PLoS ONE on 14 June 2010, the authors present evidence for a shift in the epidemic and a decline in the rate of new HIV infections in South Africa.

Applying a previously published and thoroughly validated mathematical method, prevalence data from the three national HIV surveys were used to derive estimates of HIV incidence. The availability of survey data collected in the three population-based surveys allowed, for the first time, a comparison of incidence estimates for two inter-survey intervals – for the periods 2002-2005 and 2005-2008. Overall, among adults aged 15-49, incidence declined by 35% between the two inter-survey periods. The estimate of the average annual HIV incidence rate – that means the number of new infections occurring each year among 100 susceptible individuals – for the 15-49 years age group was 2.0 % in the period 2002-2005 and declined to 1.3 % in the 2005-2008 period.

 ‘Our results imply that 1.3% of all uninfected South African adults aged 15-49 years became newly infected in the year 2007. This incidence level in the general population needs to be halved in order to meet the 2011 target of the current National Strategic Plan’, explained Rehle.

‘The study not only clearly demonstrates how serial measures of HIV prevalence can be used to estimate HIV incidence, but also shows the need to determine whether infected individuals are receiving antiretroviral treatment, he said.

One of the novelties of the 2008 survey was the detection of individuals on antiretroviral treatment (ART) by means of testing HIV positive samples for the presence of antiretroviral drugs so that the effect of treatment on HIV prevalence could be analysed. Without this information, it would not be possible to fully interpret the prevalence estimates since treatment can lead to increases in HIV prevalence without concomitant changes in incidence. Rehle et al. quantified the impact of treatment provision on the estimates of HIV, showing that the ‘excess’ prevalence due to antiretroviral treatment was 1.7 percentage points in the 15-49 age group. This means that about 440 000 HIV infected South African individuals were alive in 2008 because they were on ART and would have been dead otherwise.

Several potential factors contributing to the decline in HIV incidence were discussed in the PLoS ONE article. There is evidence from the surveys of significant increases in awareness of HIV status and condom use at last sex. There was a substantial increase in the proportion of young females aged 15-24 years who tested for HIV in the last 12 months, from 13 % in 2005 to 30 % in 2008. By 2008, more than half of 15-24 year-old females had ever been tested for HIV, compared with only one in eight previously in 2002. With respect to reported condom use, the largest increases were found among 15-24 year-old females and among 25-49 year-old males.  Shisana, a co-author explained the findings ‘Although in the study it was not possible to correlate behaviour change and knowing one’s HIV status with HIV incidence figures, through triangulation it appears that high condom use among males and females and high rates of awareness of HIV status occurred concurrently with reduction in HIV incidence.’

The scale-up of ART may have the potential to reduce HIV incidence, since effective treatment reduces viral loads and, as a consequence, the infectiousness of infected individuals. However, the authors point out that since access to treatment has only increased significantly in recent years, it is expected that such an effect would take longer to develop and require higher levels of ART coverage for an extended period of time.
The authors conclude that the estimation of the impact of ART exposure is crucial to disentangle the concurrent impact of prevention and treatment programmes on HIV prevalence. In other words, HIV prevalence may mask two success stories:

    •    reduction of HIV/AIDS mortality due to ART
    •    reduction of HIV incidence due to prevention programmes.

The key findings of this study have been presented at the 17th Conference on Retroviruses and Opportunistic Infections in San Francisco, (CROI, February 16-19, 2010), and at the National Consultation on HIV Incidence Estimation (Durban, March 24-26, 2010).

For the full article, go to http://dx.plos.org/10.1371/journal.pone.0011094