BMC Public Health 2009, 9:269 http://www.biomedcentral.com/1471-2458/9/269 ations were fitted into a final logistic regression model to determine independence in contribution of each determi- nant. This study was approved by the KEMRI/National Ethical Review Committee and research authorization obtained from The Ministry of Education Science and Technology. Informed consent was obtained by a signa- ture or finger print from parent. Assent was sought from child before finger pricking. Results General characteristics of study subjects Questionnaires and serological survey were carried out in 7 primary schools capturing 498 pupils. The study sub- jects were distributed among the schools as shown in Table 1. The age of the pupils nearly followed a normal distribution with a mean of 11.8 years, median 12 years. The proportion of males compared to females was similar (50%), with the males comprising two hundred and forty eight (248) and females two hundred and fifty (250). Only 0.2% of respondents declined participation in the study. Rubella seropositivity increased with age. Findings showed that more than half (58%) of the children were exposed to rubella by the time they attained the age of six years. The proportion increased to above 90% by the time they attained the age of fourteen years and above (Figure 1). Univariate Analysis Several potential determinants were tested in the univari- ate analysis (see additional file 1). The determinants were categorized into two: child determinants and socio-eco- nomic determinants. Weighted probability ratios were included in calculating the odds ratios (OR). Age, owner- ship of a television set, child leisure and number of sib- lings were strongly associated with rubella seropositivity computed in the univariate analysis. Multivariate analysis A multivariate logistic regression model was used to deter- mine which factors among those that showed significant Table 1: Characteristics of study subjects Participants Males Females School Kapkorren Maendeleo Bwayi Kwenet AIC Tenai Mukunga Jabali Total 84 75 83 69 61 60 66 498 46 37 38 35 30 33 31 250 38 38 45 34 31 27 35 248 association with rubella seropositivity in univariate anal- yses contributed independently to the association. Working adults residing with family showed marginal insignificance (OR 2.08, 95%CI 0.90–4.8, p = 0.076) in the univariate analysis and was included in the final logis- tic regression model. The model controlled for the con- founding influence of each variable. Only age and ownership of a television set remained significant in the final logistic regression model. Table 2 shows the odds ratios for the association of the various determinants with rubella seropositivity in the final logistic regression model. The age of the child was strongly associated with rubella seropositivity and the odds ratios for age as a continuous variable was 4.0 (95% CI 2.46–6.53). A child whose family did not own a televi- sion set had three times increase in odds when compared to a child whose family had a television set (OR 3.3, 95%CI 1.45–7.48). The other variables that are child lei- sure, number of siblings and working adults residing with family that had showed significance in the univariate analyses lost significance when fitted in the logistic regres- sion model and were considered as confounders (Table 2). Discussion Presence of rubella specific IgG in an unvaccinated popu- lation is a long-term marker of previous infection, which helps to assess the immune status of that population. No study has been conducted in Kenya to assess seropreva- lence rates in children or in adolescents. The school-based study captured pupils aged 4–20 years and was fairly exhaustive as it reflected on age-specific seroprevalence rates through a wide age range. In 2003, the Kenyan gov- ernment passed a policy to provide free and compulsory primary school education. The outcome was high influx of fairly older pupils in public schools. The children who were yet to attend school were not captured in this study. Many factors potentially influence rubella seropositivity in children. In this study age and ownership of television set were identified as significant factors in the acquisition of rubella antibody. Child related factors such as gender, history of travel outside district, history of rash illness and involvement in extra-curriculum activities appeared to be insignificant factors. Comparison with other studies may be required. Socio-economic factors such as level of edu- cation, occupation and type of housing appeared not to be significantly associated with rubella antibody acquisi- tion among children. Ownership of a television set seemed to reflect more on the socio-economic status of family in this community. The likely reason for this find- ing is that the main source of income in this community Page 3 of 5 (page number not for citation purposes)