HIV prevalence figures reflect the proportion of people in the population living with HIV at a given point in time. The observed HIV prevalence is the result of cumulative new infections over time, minus the cumulative deaths that occurred in HIV infected persons. HIV prevalence includes past and recent infections.
In the 2005 South African national household survey on HIV Prevalence, Incidence, Behaviour and Communication, another important measurement was added, namely incidence. In contrast to prevalence, HIV incidence quantifies the number of new infections that occur in non-infected individuals during a specified period of time, e.g. the annual incidence during a given year.
The complexities and limitations of epidemiological approaches to measure national HIV incidence in large cohort studies made a case for a laboratory-based method that can distinguish recent from established long-term HIV infections. The availability of tests for recent HIV infection promises to be a major advance in estimating incidence in selected populations. Incidence measures are generally better than prevalence measures for assessing the dynamics of HIV transmission in different population strata. The addition of HIV incidence testing into the 2005 survey protocol enables us for the first time to analyze HIV prevalence estimates, HIV incidence estimates and HIV associated risk factors concurrently.
Current HIV-transmission dynamics in South Africa are best reflected by the HIV-incidence figures observed in the different sub-populations. Especially alarming are the incidence rates among young females at prime childbearing age. Women in the 15-24 age group have an eight-times higher HIV incidence than males (6.5% compared to 0.8%) and account for 87% of the recent HIV infections in this age group.
Our incidence analysis also confirmed recent findings from Uganda by Gray et al. (2005) that suggest an increased risk of HIV acquisition during pregnancy. Among African women aged 15-49 years who were pregnant in the last 24 months an HIV incidence of 7.9% was found, the highest incidence rate of all analysed sub-populations in our survey. This is powerful information in developing prevention interventions specifically targeted at pregnant women visiting antenatal clinics.
Almost 16 000 specimens tested for HIV provided an unparalleled large sample to estimate HIV incidence on a national scale for South Africa. Table 3.18 presents HIV incidence estimates for the main reporting domains of the 2005 survey:
Table 3.18: HIV incidence among respondents 2 years and older by background characteristics, South Africa 2005