The study by Rehle et al. in this issue of the SAMJ makes an important contribution to understanding the dynamics of the HIV epidemic in South Africa. While the high prevalence of HIV confirms that HIV continues to be hyper-endemic in South Africa their estimates of HIV incidence highlight the extraordinarily high levels of ongoing HIV transmission in South Africa. A deep concern is the unrelenting epidemic in youth with particularly high incidence rates in young women. In their study Rehle et al. utilise the IgG-Capture BED enzyme immunoassay (BED-CEIA) to detect recent HIV seroconversion for the purpose of calculating HIV incidence rates. This technology has been applied to several cross-sectional surveys to estimate incidence including an injecting drug user population from Bangkok. Since this method is still being validated for different conditions such as viral clade the absolute estimates of incidence should be regarded as tentative but the subgroup comparisons in the study remain highly informative. In order to understand the dynamics of HIV infection and epidemic trends more data are needed on the current burden of disease the rate of new HIV infections and mortality rates. At a time when prevalence trends in pregnant South African women suggest that incident cases of HIV infection are being masked by rising mortality it is of particular importance to monitor changes in the number of new infections in South Africa. (excerpt)