TAC is concerned about methodological discrepancies in 2007 antenatal survey
Nevertheless, there is evidence of a decline in new infections among youth
The TAC notes the publication of the 2007 antenatal survey. We have been alerted to some concerns with the way the survey results, particularly provincial and national prevalence, have been calculated. Nevertheless, a positive result of the survey is that there is evidence of a decline in new infections among youth.
It has been explained to TAC by some of South Africa's leading demographers that the provincial and national prevalence reported in the antenatal survey for 2007 appears to have been calculated using a different methodology to 2006. The apparent decline in provincial and national prevalence in 2007 may therefore be a consequence of this change in methodology. Provincial prevalence is calculated using district prevalence. A comparison of antenatal prevalence at district level between 2006 and 2007 indicates that, if anything, there has been no decrease in prevalence. It is not necessarily wrong for the Department of Health to change its calculation methodology if it has a reasonable basis for doing so but by failing to state that it has done so in the report, it has made a mistake or misled the public into thinking a real decline in prevalence has been measured. Furthermore, it appears that the methodology to measure prevalence in 2006 might also be different to 2005, possibly rendering comparisons over that period problematic too. The failure to adequately explain these methodology changes and why they were done is poor science and renders the antenatal survey a much less useful source of data than it could otherwise be.
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 (emigration can affect prevalence too, but this is not relevant for South Africa). It has become extremely difficult to interpret the meaning of prevalence in recent years for two reasons: the HIV epidemic has matured into an AIDS epidemic (with more people dying) and antiretroviral treatment is helping people with HIV to live much longer. These two opposing effects confound our understanding of prevalence. It has become very difficult to understand how the antenatal and overall prevalence rates relate to new infections.
At this point in the HIV epidemic, the key measure of HIV prevention success is incidence, i.e. the rate of new infections. However antenatal prevalence among youth is a useful indicator of incidence in this age group. A positive aspect of the antenatal survey is that there does appear to be a decline in prevalence among youth and this indicates that there is likely a decline in new infections (i.e. incidence) among youth, however incidence among youth remains far too high.
Later this year the Human Sciences Research Council is expected to release an incidence study. This hopefully will give us a much better picture of the trajectory of the epidemic.
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.
TAC usually produces an analysis of the antenatal survey a week after it has been released. Given the above discrepancies, we will be delaying this.
For more information call Lesley Odendal on 072 174 1204