The HIV sentinel surveillance data has helped to map the epidemic and monitor HIV infection trends in the country and has served as an advocacy tool, resulting in the mobilization of partners, resources and development of innovative approaches by the national response to HIV and AIDS. The 2011 HIV survey was the 22nd round to be conducted in the country by the Department of Health.
The South African antenatal clinic survey is done annually in October to obtain an estimate of the point prevalence for that year. The data set generated from this survey is used by mathematical modelers such WHO/UNAIDS reference group and others to estimate the rate of new HIV infections (incidence) and HIV-associated deaths are derived through mathematical models applied to HIV prevalence estimates.
The Department of Health will continue to sustain and enhance the use of this robust Unlinked anonymous HIV surveillance methodology to monitor the HIV epidemic trend in South Africa through conducting annual HIV antenatal sentinel surveillance at national, provincial and district levels.
The HIV epidemic in South Africa has in the last 6 years shown stabilization, particularly among antenatal care first time bookers in their current pregnancy served in public health sector clinics.
In 2011, a total of 33 446 first time antenatal care attendees participated in the survey. This was a representative sample to make conclusive inferences on the HIV and syphilis occurrence at National and Provincial level and in all 52 Health Districts.
The survey epidemiological design uses a cross-sectional unlinked anonymous testing method using blood samples collected for other purposes in selected sentinel primary health care facilitates. This sampling approach is convenient because, as part of the antenatal care services it is mandatory to routinely draw blood from the first bookers, and this minimises participation bias and reduces costs.
In addition, pregnant women are universally the most common Sentinel Population for HIV and in South Africa the most common mode of transmission is the heterogeneous sexual route.
It is not perfectly representative of all women and even less of men, children and non-pregnant women, but it is an important means of coverage for countries that have a generalized HIV epidemic (i.e. where HIV prevalence among pregnant women is >2%) and it also has a wide geographic coverage (urban; informal settlements and rural communities).
Intravenous blood samples are collected from the pregnant first bookers in their current pregnancy, recruited from 1 445 public sector antenatal clinics every month of October since 1990. Their full intravenous blood specimens were collected and sent to central pathology laboratories in the various provinces for HIV and syphilis analysis.
The laboratory diagnostic test used were the highly specific and sensitive Enzyme Linked Immuno Sorbent Assay (ELISA) for HIV antigen testing and the Rapid Plasma Reagin (RPR) card test for active syphilis.
Given that the sentinel sites were chosen on a probability proportional to size basis by district, the sampling period was fixed and the districts samples were self-weighting, the provincial prevalence estimates were calculated as the total of the results from the districts in the provinces.
The national prevalence was weighted according to the total number of women aged 15 - 49 years in each province using the 2011 midyear population size estimates.
The sentinel population (participants) who agreed to participate in the survey has increased from 32 255 in 2010 to 33 446 in 2011 of the targeted 36 000 pregnant women attending antenatal care. The sample population realization rate in 2011 was 92.9% which exceeds 70% compliance as outlined in the survey protocol.