BMC Public Health 2009, 9:269 http://www.biomedcentral.com/1471-2458/9/269 Background Debate on whether or not to introduce rubella vaccina- tion has continued to mount in many countries. While the vaccine is widely used in the developed countries, there are concerns about safety in countries with limited resources [1]. Rubella infection during pregnancy may result in the delivery of a child with congenital rubella syndrome (CRS). Infection acquired in the first trimester of pregnancy poses high risk of CRS to the unborn child. Congenital infection with rubella virus can affect all organ systems but the most common and often the sole mani- festation of this infection is deafness. Eye defects may also occur and includes cataracts, glaucoma, retinopathy and microphthalmia [2,3]. Other life threatening complica- tions include heart defects such as patent ductus arterio- sus. The ultimate aim of rubella vaccination is to eliminate occurrence of CRS [4]. Congenital rubella syndrome is not well characterized in many regions especially in develop- ing countries. Kenya lacks current and conclusive data on prevalence of rubella and extremely scanty data on inci- dence of CRS. A small study conducted on gravid women attending Kenyatta and Aga Khan hospitals in Nairobi, at the time of delivery in early 1980's did not address rubella susceptibility in children and adolescents [5]. In most developing countries with no vaccination pro- gramme, rubella epidemics occur periodically 4–5 years. Emerging evidence from the Kenya Integrated Disease Sur- veillance and Response department (DDSR) through measles surveillance programme, suggests widespread rubella endemicity in the country. Through an active mea- sles surveillance system, an average of 400 rubella cases are confirmed annually countrywide but this could be underestimated (DDSR measles database). Availability of these data in addition to public awareness on the inherent risks posed by rubella infection have led to mounting pressure on health workers within the Ministry of Health to consider introduction of rubella vaccine in the routine primary health care. Whereas measles surveillance pro- vides an opportunity to conduct passive rubella surveil- lance by testing measles suspected cases for rubella, well- designed studies are inevitable in attempting to provide scientific evidence on the burden of disease [4,6]. This study was designed to determine age-specific rubella sero- prevalence rates and to assess potential risk factors associ- ated with rubella seropositivity among school attending children. Rubella infection in children is not a major health concern and direct measurement of CRS burden can be done among pregnant women but the data is not sufficient without information on seroprevalence rates of children. Virus circulation often begins among the chil- dren; as a result a few susceptible pregnant women can be infected [7]. The aim of this study was to determine the age-specific rubella seroprevalence and the factors that influence exposure in pre-and primary school attending children in Uasin Gishu district, Moi's Bridge location. No study has been conducted among these age-groups in Kenya and the results will provide pre-vaccination data that will be used to model rubella incidence and impact of vaccination when introduced [4,8]. The study was a cross-sectional school-based survey. The survey captured primary and pre-primary school going pupils (age 4–20 years). Methods This study was conducted in Moi's bridge location, Soy division, Uasin Gishu district, and approximately 40 km North of Eldoret town during the months of February– March and May–June 2005. Sample size was calculated using EPI INFO 3.2.2 statistical package. A 95% confi- dence interval, a study power of 80% and prevalence of 50%, with 3% precision was used. A 20% non-response rate was factored in. To ensure the representativeness of the locality, we selected 7 schools through guidance of the District Education office, Uasin Gishu. The survey was done using multistage cluster sampling. Initially, schools were selected using an area-sampling approach to ensure spatial distribution within a location, which had 16 schools [9]. Pupils in each school were selected by systematic sampling using student enrolment registers. A standard structured questionnaire was administered to survey the general characteristics. Parents completed the questionnaire with the aid of interviewers. After obtaining consent from parent, finger prick blood (Dried Blood Spot) was obtained and spotted on labeled S$S® filter paper from every child who assented. The spots were allowed to dry before packaging in zip-lock bags. They were left overnight at room temperature and shipped to KEMRI laboratory where they were placed at +2–8°C until testing. Samples were screened for rubella-specific IgG antibodies using commercial immunoassay kits, Enzyg- nost® (Behring, Germany). Manufacturer's instructions were followed for the procedure except for additional 15 minutes incubation time for conjugate step procedure. This additional time was used after optimization was done using paired samples (sera and dried blood spots from same individual). Sample buffer supplied with kit was used to elute blood spots. The data was analyzed using EPI INFO version 3.3.2. Man- tel-Haenzel 2-tailed P and Fisher exact test. All tests were at 5% probability level. Odds ratios were computed for each potential determinant and those that showed associ- Page 2 of 5 (page number not for citation purposes)