HIV prevalence drop - fact or fiction?

A few problems with the recently released 2007 National HIV and Syphilis Prevalence Survey [PDF] aka Antenatal Survey.

It appears that the new stats have been produced using a new methodology to work out its conclusions.

Two people who know what they're talking about when it comes to these stats wrote a letter to the SAMJ, which can be found here [PDF].
The new weighting gives rise to some absurd results. For example, the prevalence in the Western Cape, which previously had the most rapidly growing epidemic, albeit from a low base, apparently fell from 15.1% in 2006 to 12.6% in 2007. This while, apparently, prevalence fell in only two districts, and in both cases by less than 1%, and in the presence of a significant roll-out of life-preserving treatment which would, other things being equal, lead to an increase in the numbers of infected women in the province.

Rob Dorrington, David Bourne. Has HIV prevalence peaked in South Africa? – Can the report on the latest antenatal survey be trusted to answer this question?  SAMJ October 2008, Vol. 98, No. 10

Reported here by IRIN:
After recalculating the 2007 figures, using the same method applied to the 2006 data, the authors estimated HIV prevalence among pregnant women at 29.4 percent. Antenatal prevalence figures are used in combination with other surveys and mathematical models to determine HIV prevalence in the overall population, but the revised figure suggests that the number of South Africans living with HIV has probably not declined. ...

Dorrington and Bourne conclude that "analysis of these data appears to be becoming increasingly beyond the skills of the Department of Health" and recommend that the government enlist the help of the broader scientific community to help interpret future figures on prevalence.

Reported here by the Treatment Action Campaign.
The Minister of Health has touted the drop in HIV prevalence as a success. Her claims must be treated with scepticism. Nevertheless, a slight increase in prevalence would not indicate a worsening HIV epidemic. Prevalence measures the total number of HIV positive people at a specific time. A decrease in prevalence for the whole population can only occur if more people with HIV die than become infected ...

At this point in the HIV epidemic, the key measure of HIV prevention success is incidence, i.e. the rate of new infections. ...

TAC calls upon the South African National AIDS Council (SANAC) to assist the Department of Health with the analysis and interpretation of the results of the antenatal survey.

TAC calls upon the Department of Health to release the details and rationale for the methodologies used to calculate provincial and national prevalence from district data for its 2007, 2006 and 2005 antenatal prevalence studies.

A note on the correct use of the terms "method" and "methodology" which do NOT mean the same thing:
A fondness for big words isn't always accompanied by the knowledge of their proper use. Methodology is about the methods of doing something; it is not the methods themselves. It is both pretentious and erroneous to write "The architect is trying to determine a methodology for reinforcing the foundation now that the hotel on top of it has begun to sink."


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