BMC Public Health 2006, 6:109 http://www.biomedcentral.com/1471-2458/6/109 Background Surveillance of human immunodeficiency virus (HIV) infection among pregnant women attending antenatal care clinics (ANC) has been the mainstay system of mon- itoring of HIV epidemic in most countries of sub-Saharan Africa [1-5]. Several studies from the 1990s showed that ANC based prevalence estimates approximated preva- lence levels in the population of men and women aged 15–49 years [6-10]. However, the validity of prevalence estimates based on national ANC surveillance systems will depend on how accurately the selected sentinel sites represent the whole population [11]. In many resource- constrained countries, the quality of surveillance had been questionable for various reasons. It is common to find an uneven distribution of sentinel surveillance favouring sites mostly in urban and semi-urban areas [12,13]. This has led to limited surveillance information from rural areas, especially those that are inaccessible due to difficult terrain and lack of roads, and where literacy levels are generally low. These scenarios complicate attempts to determine the real magnitude and trends of HIV infection in different population groups, and make it difficult to develop appropriate preventive and control measures. Very difficult terrain, poor roads and infrastructure, lim- ited health facilities, and low literacy and socio-economic levels characterise the rural areas of Manyara and Singida regions within northern Tanzania. Since 1955, one of the main health providers of these rural settings has been the Haydom Lutheran Hospital (HLH), which is a 400- bed hospital owned by the Evangelical Lutheran Church of Tanzania (ELCT). The hospital works closely with national, regional and local government and health authorities, and offers its services within the national health plan, using national guidelines. In September 2002, the Haydom Lutheran Hospital, with funding from the Royal Norwegian Embassy in Dar es Salaam, Tanzania, initiated a multi-sectoral collaboration for a comprehensive HIV prevention-intervention pro- gram. The project aimed to reduce the risk of HIV trans- mission; vulnerability of HIV infected persons and impact of HIV in the catchment area [14]. Generating local knowledge on the epidemiological con- text of HIV infection is of critical importance to plan inter- ventions in the area. We present results from the antenatal clinic-based sentinel surveillance from various rural sites in Manyara and Singida regions in 2003/2004. Methods Study area We conducted this study from November 2003 to April 2004 within the catchment area of the Haydom Lutheran Hospital (HLH), located in Mbulu district of Manyara region within Northern Tanzania. The area constitutes three administrative divisions in the rural areas of two regions of Manyara and Singida. In Manyara region, we included two divisions, namely Dongobesh division from Mbulu district and Basotu division from Hanang district. From Singida region, Nduguti division from Iramba dis- trict was included in the study. Based on the 2002 census [15], with extrapolation to 2003 of 3.8% annual growth for Manyara Region and 2.3% annual growth for Singida region, the three rural divisions had a total population of 259,292 persons. In the study area, all four main language groups of East Africa are represented. The Iraqw (Cushitic), Datoga (Nilotic), and Iramba (Bantu) are the largest groups, although the commonly spoken language is Kiswahili. The main economic activities in the area are subsistence farming and pastoralism. The HLH provides the main hospital level health care in the area. Sampling Geographical stratification of the area into two strata (remote rural and rural) for each division (smaller units of a district) enabled us to conveniently sample two sentinel sites from each division, one from remote rural and one rural site. Six sentinel sites (three from remote rural and three from rural) within the three divisions were included in the study. The three rural clinics were the HLH clinic, the Nduguti Dispensary (government) and the Basotu Dispensary (government). From the remote rural areas, we had two HLH owned outreach clinics from Muslur (Dongobesh division) and Dangayda (Basotu division) and the Roman Catholic owned Mwanga Dispensary (Nduguti division). The selected sentinel sites provided adequate sample size and representative pregnant women within the catchment area based on sample size estimates [16]. We defined a "rural" residential area in this study as villages within the catchment area with more than two general utility shops and an established health facility. While "remote rural" villages are those found in the remote difficult terrain. Usually, these remote areas lack established health facilities or utility shops. Residents from remote rural areas have to travel by foot at least an average of 3 hours to get basic health services and at least 7 hours to the nearest hospital [17]. Sample size The sample size was estimate based on Statcal calculation of Epi Info computer package for descriptive studies ver- sion 6 [18]. Using the hospital based population preva- lence of 2% [14], an estimate of 1000 pregnant women was considered adequate to detect the prevalence of HIV. We used the expected prevalence of 2% and worst accept- Page 2 of 9 (page number not for citation purposes)