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Ideally, HIV spread and changes over time should be tracked through measuring the number and distribution of new infections, or incidence, in a population. Incidence estimates reflect the underlying HIV transmission dynamics that are currently at work in South Africa. The availability of laboratory-based tests for recent HIV infection signals a new era in HIV surveillance, and now offers a direct measure for tracking the epidemic and evaluating the impacts of prevention interventions. In an article by Thomas Rehle et al. in the March 2007 edition of the South African Medical Journal (SAMJ), an unparallelled large sample of 15 851 blood specimens was analysed to estimate HIV incidence on a national scale for South Africa. The detection of recent infections was performed on confirmed HIV-positive samples, using the BED capture enzyme immunoassay optimised for dried blood spot (DBS) specimens. BED HIV incidence calculations applied adjustment procedures that were recently revised and approved for subtype C blood specimens, the predominant HIV subtype in Southern Africa. The analysis was based on data from the South African National HIV Prevalence, HIV Incidence, Behaviour and Communication Survey, 2005, commissioned by the Nelson Mandela Foundation with additional support from the US Centers for Disease Control and Prevention. HIV incidence in the population aged two years and older was 1.4%, with 571 000 new HIV infections estimated for 2005, translating roughly into 1 500 new infections per day. An HIV incidence rate of 2.4% was found among individuals aged 15-49 years. Of all new HIV infections, 34% occurred in young people in the 15-24 age group. The incidence rates among young women in the prime childbearing age are especially alarming. The HIV incidence in the age group 20-29, was 5.6%, 6 times more than in males of the same age (0.9%). Among young people in the 15-24 year age group, women accounted for 90% of all recent HIV infections. ‘These findings suggest that the current prevention campaigns do not have the desired impact, particularly among young women’, concluded Professor Thomas Rehle, Director in the Social Aspects of HIV/AIDS and Health research programme at the Human Sciences Research Council (HSRC). The incidence analysis also shows that a substantial number of new non-vertical infections (i.e. not transferred from mother to child) have occurred among children in South Africa, ’The causes of these non-vertical transmission still need further investigation using longitudinal designs that help us understand cause and effect’, said Dr Olive Shisana, President and CEO of the HSRC and a co-author of the paper. Another important epidemiological aspect of the disease is place of residence. People living in urban informal settlements have by far the highest incidence rates (5.1%), followed by those living in rural informal areas (1.6%, rural informal areas (1.4%) and urban formal areas (0.8%). ‘These results suggest that poverty plays a significant role in increasing vulnerability to HIV.’ said Dr Shisana. The analysis of condom use at last sex by age group illustrates that HIV incidence is a more appropriate measure than HIV prevalence to interpret the behavioural effects on HIV infection. ‘An encouraging finding of the study was that reported condom use at last sex in the younger age group is associated with substantially lower HIV incidence, particularly among young males’, emphasises Dr Victoria Pillay, a research specialist at the HSRC and a co-author of the paper. A surprising finding was the high incidence among widowed individuals, who had a remarkably high incidence of HIV of 5.8%, especially among women. Pregnancy is a significant risk factor for HIV. The article says the analysis supports recent findings from Uganda that suggest an increased risk of HIV acquisition during pregnancy. Of the women in the 15-49 age group who reported a current pregnancy, 5.2% were found to be newly infected, compared with 3.7% in the non-pregnant female population in this age group. ‘Incidence data provide critical new insights into the dynamics of the HIV epidemic and are a more appropriate measure to correlate biological data with recent behaviours or recent behavioural changes. The 2005 national HIV incidence estimates presented in this study will serve as benchmark figures for future assessments of the dynamics and trends of the South African HIV epidemic’ explained Professor Thomas Rehle. The national HIV incidence measures – new insights into the South African epidemic  , Thomas Rehle, Olive Shisana, Victoria Pillay, Khangelani Zuma, Adrian Puren and Warren Parker (SAMJ, March 2007).
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