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New HIV/AIDS model reflects significant impact of interventions
Actuarial Society of South Africa Press Release. July 2004.
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Today the Actuarial Society of South Africa released the most recent version of their AIDS and Demographic model for projecting the impact of HIV/AIDS on the South African population. The model, known as the ASSA2002 model, predicts that some five million South Africans are currently infected with HIV. This is about 25% lower than previous estimates. The lower estimates are mainly due to improvements to the model to incorporate more up-to-date evidence that the relationship between antenatal prevalence and general population prevalence in South Africa is not the same as that observed in other African countries, where fertility is much higher than it is in South Africa. However, it is also due in part to the fact that the new model allows for interventions that have been in place for some years (such as increasing use of condoms and improved treatment of STDs).
Apart from improved estimates of the extent of the epidemic, the main development in ASSA2002 is to incorporate the impact of interventions. Five interventions have been modelled: information and education campaigns, improved treatment of sexually transmitted diseases, voluntary counselling and testing, mother to child transmission prevention and antiretroviral treatment. This makes the model much more relevant at a time when both the public and private sectors are rolling out various interventions.
The model shows that interventions have had and are having a significant impact on the course of the epidemic, and that the extent of the national antiretroviral treatment programme in the future will play a particularly important role in the future outcome of the epidemic. For example, the model estimates that by 2010, there are likely to be roughly 380,000 AIDS deaths per annum. However, the number could be anywhere between 290,000 and 450,000, depending on the extent of the national antiretroviral treatment programme.
In addition, the model now produces estimates of the number of HIV-infected people in the different stages of disease, which is useful in assessing the extent of the morbidity associated with the epidemic. The model estimates that currently roughly 10% of people with HIV (i.e. half a million South Africans) are sick with AIDS.
Furthermore, life expectancy at birth is now expected to fall to a little below 50 years and then plateau around this level. Previous estimates suggested that life expectancy would fall to around 43 years before climbing back up to level off at around 50 years.
According to David Schneider, convener of the ASSA AIDS Committee, "we believe the ASSA2002 model is a landmark achievement in understanding the South African HIV/AIDS epidemic and improving the accuracy of our demographic estimates."
According to Prof. Rob Dorrington, UCT professor of actuarial science, demographer and a key developer of the model, "there is always some degree of uncertainty about predicting the future. Data on the HIV/AIDS epidemic in South Africa are scarce so we need to use the imperfect information that we have to forecast the future."
More information was available for the ASSA2002 model than was available for the ASSA2000 model. In particular, the results of two more annual antenatal clinic surveys were available, as well as more recent death data from the Department of Home Affairs and the Human Sciences Research Council survey on HIV prevalence in households.
While the reduced estimates are good news, Dorrington warns that "by 2010, despite interventions and treatments, we estimate that nearly 3.5 million South Africans will have died of HIV/AIDS related causes. Whether it turns out to be 2.9 million or 3.8 million in practice, we still have a major challenge on our hands."
The ASSA2002 model is publicly available on ASSA's website (www.assa.org.za) and has relevance to a variety of users, including demographers, government, those who make decisions on health policy, economists, actuaries, health care professionals, academics researching HIV/AIDS, underwriters and journalists. Over 400 people are registered users of the model.
According to Dorrington, "the model is provided in the public domain, and in open source code, so that users are free to download, critically review the model and question its structure and methodologies. It is hoped that in so doing, ASSA can further research and improve the modelling of the epidemic." |
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