Belyhun et al. BMC Public Health 2010, 10:21 http://www.biomedcentral.com/1471-2458/10/21 version 3. Analysis was performed using SPSS version 12.0.1 (SPSS Inc. Chicago, IL). The dependent variables were any STH infection in the mother and any STH infection in the child (where STH infection is taken to mean infection with any of A. lumbricoides, T. tri- chiura, hookworm or S. stercoralis). Potential risk fac- tors explored were demographic factors (gender, mother’s age, urban/rural place of residence and ethni- city), markers of social advantage (education, occupa- tion, home ownership and TV/radio ownership) and factors associated with housing and lifestyle (roof type, type of toilet, water source, animals in the home, place of cooking, soap use, and waste disposal method). Initially the univariate association between each expo- sure and the presence of infection was assessed using the Chi-squared test and odds ratios were computed as measures of association. To determine the independent risk factors for infection, logistic regression analysis was employed. Variables were manually added and removed from the model until only those that signifi- cantly improved the model remained. Urban/rural place of residence and gender (child model only) and additionally age of the mother (maternal model only) were treated as a priori confounders and retained in the model regardless of significance. Ethical consideration Approval for this study was granted by the Ethics Com- mittee of the Aklilu Lemma Institute of Pathobiology, Addis Ababa University. All mothers and children with STH infections were treated with anti-helminthics based on the national protocol. Results Description of the study subjects Nine hundred thirty two child-mother pairs were fol- lowed up at one year, and 908 (97.4%) of the mothers Table 1 Prevalence of soil-transmitted helminth infections in mothers and their infants in the Butajira birth cohort, Ethiopia, 2007 Soil-transmitted helminths Hookworms Ascaris lumbricoides Trichuris trichiura Strongyloides stercoralis Any soil-transmitted helminth infection Prevalence of single infection Prevalence of double infection Prevalence of triple infection N = total number of study participants Children (N = 905) Mothers (N = 908) No (%) No (%) 21 (2.3) 328 (36.1) 13 (1.5) 80 (8.8) 4 (0.4) 30 (3.3) 10 (1.1) 29 (3.2) 44 (4.9) 395 (43.5) 40 (4.4) 4 (0.4) 0 (0) 329 (36.2) 60 (6.6) 6 (0.7) Page 3 of 7 and 905 (97.1%) of their infants provided adequate stool samples and were included in the analysis (Fig 1). The majority were from rural areas (87%) and there were roughly equal numbers of male (460; 50.7%) and female (448; 49.3%) infants. The age range of interviewed mothers was 15 to 44 years (mean, standard deviation [SD] 26.8 [6.3] years), with almost one third (38.7%) aged under 25. Prevalence of soil-transmitted helminths Four species of soil-transmitted helminths (STHs) were identified in the stool samples, with the overall preva- lence of any STH infection being 43.5% (95% confidence interval (CI) 40.2-46.8%) in mothers, and 4.9% (95%CI 3.6-6.5%) in children, respectively (Table 1). Hookworm was the predominant intestinal helminth infection, detected in 36.1% of mothers and in 2.3% of children, and A. lumbricoides was the second most frequently detected intestinal parasite with prevalence of 8.8% in mothers and 1.5% in children (Table 1). About one third (36.2%) of mothers and 4.4% of children had a sin- gle infection, while 6.6% of mothers and 0.4% of chil- dren had double infections, 0.7% of mothers had triple infections (Table 1). Univariate risk factor analysis for STH infection in mothers The distributions of the demographic and lifestyle fac- tors of the subjects are shown in Tables 2 and 3. In uni- variate analyses, significant positive associations were seen between presence of any STH in the mother and living in a house with a thatched roof (Odds Ratio (OR) 1.62; 95% CI 1.18-2.24, p = 0.003), home ownership (OR 1.67, 95% CI 1.04-2.68, p = 0.033), cooking inside (OR 1.68; 95% CI 1.18-2.37, p = 0.003) and for disposing waste in open field relative to burying or burning (over- all p = 0.013, OR 1.66; 95% CI 1.23-2.46). In addition, frequency of soap use was significantly associated with maternal infection with increased risk seen for infre- quent soap users compared to daily use (overall p = 0.008, OR 1.51, 95% CI 1.14-2.01). A significant negative association was found in relation to urban living (OR 0.48; 95% CI 0.32-0.73, p = 0.001), whereas the associa- tion with education level was only of borderline signifi- cance (p for trend = 0.051 OR 0.71; 95% CI 0.51-1.00) (Tables 2 and 3). Univariate risk factor analysis for STH infection in children Significant univariate associations were identified with cooking site (OR 0.43; 95% CI 0.23-0.83 for inside rela- tive to outside, p = 0.012), living in a house with a thatched roof (OR 0.51; 95% CI 0.27-0.96, p = 0.037) and with household source of water (overall p < 0.001) such that the greatest prevalence of infection was