Belyhun et al. BMC Public Health 2010, 10:21 http://www.biomedcentral.com/1471-2458/10/21 technique was not performed due to issues related to feasibility. However, the results are unique in that they arise from a population based cohort, and provide valu- able information on prevalence and risk factors among infants in a low-income setting. The prevalence of STH infection observed in mothers (43.5%) was higher than that reported previously (33.8%) in a random sample of the Butajira Rural Health Project [18]. In this previous study, hookworms were found in 14.7% of the study population, lower than in our mothers (36.1%) while A. lumbricoides was found in a higher proportion of the general population (16.6%) than in our mothers (8.8%). The low prevalence of hookworm in the previous study may be because the earlier study population was on average younger than the mothers in this study (median age 20 vs. 26 years). Moreover, the previous study consisted of a significantly higher proportion of urban participants, who live in houses with corrugated iron roofs, and were more edu- cated than the birth cohort women. All these factors might explain the lower prevalence of hookworm infec- tion in the earlier study [18]. Multiple STH infections were also less common than in other studies in Ethiopia. Studies in the south and areas around Wondo-Genet report 80% of populations to be infected with one helminthic parasite, 40% with two, and 3% with four [19,20]. Such differences might arise from differences in study subjects, socio-demo- graphic conditions of the society or differences in the parasitological examination techniques. The prevalences of hookworm (2.3%) and A. lumbri- coides (1.5%) in our infants were much lower than those found among one year-old children in Jimma, Ethiopia, (hookworm 13.3%, A. lumbricoides 35.0%, [21]). The lower prevalence of STHs in children in this population is probably linked to the Enhanced Outreach Strategy (EOS) for child survival, a mass de-worming interven- tion started in 2006 in under-five children in this area [5]. Even though we were not clearly able to ascertain whether the deworming included our study participants, the intervention might have changed the parental health related behavior or siblings in the household might have received the medication further reducing transmission. This study showed that maternal hookworm infection was more prevalent (36.1%) than other STH infection. In their review, Hotez et al indicated that 30% of Ken- yan, 41% of Nepalese, and 53% of Vietnamese women of reproductive age had a hookworm infection [2], higher than other STHs and comparable to this study. This may be explained by the fact that women spend more time than men in muddy, wet gardens suitable for third stage infective hookworm larvae. Women in the Butajira area spend much of their time in farm plots and wet gardens covered by false banana, Khat and coffee trees Page 6 of 7 that may all contribute to the survival of hookworm lar- vae. The higher prevalence of hookworm infection in adulthood may also be explained by the nature of the parasite-host relationship [2]: unlike other soil-trans- mitted helminths, hookworms secrete many bioactive polypeptides which dampen down host immune responses [2]. The present study also assessed the possible associa- tion of STH infection with potential risk factors among mothers and children in the cohort. Several recent stu- dies have identified a range of environmental and social risk factors associated with STH infections [22-24]. However, very few of the environmental and socioeco- nomic factors were significantly associated in this study; making it comparable to earlier studies in Ethiopia and other less developed countries [23,25,26]. One of the factors strongly protecting against maternal helminth infection in this study was daily use of soap by the mothers. It was not the presence of soap in the house- hold but the frequency of its use that protected from STH infection. Several studies have shown a significantly higher prevalence of helminth infection among subjects who rarely washed their hands with soap compared to those who washed their hands regularly [22,25-27]. The other factor protecting mothers from helminth infection was urban residence. This is likely to be related to the lower prevalence of sanitary measures in the rural areas of Ethiopia. For instance, the proportion of the population with access to an improved water source is nearly twice as high in urban as in rural areas [13]. In addition, access to improved sanitation is four times higher in urban than rural areas [13]. Interven- tions to reduce helminth infection must focus on rural residents. This study also found that using water from a pipe inside a compound was a risk factor for helminth infection in infants. Other studies have shown that hel- minth infection among pipe users in underdeveloped countries may arise from the poor quality of piped water [28,29]. Efforts to minimize microbial contamina- tion of piped water supplies and to monitor water qual- ity are important. However, other unknown factors may contribute to the increased risk associated with piped water and merit further investigation. Conclusions STH infection is common in mothers in this low- income birth cohort. Risk factors associated with infec- tion suggest that mass de-worming strategies must also address provision of safe water and health education about soap use, particularly among rural residents. Acknowledgements We thank the technicians of Aklilu Lemma Research Institute of the Medical Parasitology unit for examining the stool samples. We also thank the