Risk factors for infection with soil-transmitted helminths during an integrated community level water, sanitation, and hygiene and deworming intervention in Timor-Leste

Water, sanitation and hygiene interventions have been advocated as important complements to deworming programs to improve soil-transmitted helminth control. Evidence for the impact of water, sanitation and hygiene on soil-transmitted helminth infections is mixed, and based mainly on cross-sectional studies. In this study, we assessed associations between individual- and household-level water, sanitation and hygiene variables and soil-transmitted helminth infections, using data collected during the 2 year follow-up study period of the WASH for WORMS randomised controlled trial in Timor-Leste. Data were collected across four surveys, conducted at 6 monthly intervals in 23 communities. We analysed water, sanitation and hygiene and sociodemographic variables as risk factors for infection with Necator americanus, Ascaris spp., and undifferentiated soil-transmitted helminth infection, using generalised linear mixed models to account for clustering at community, household and participant levels. Water, sanitation and hygiene risk factors were examined both concurrently and with a 6 month lag period that coincided with the most recent deworming. The analysis included 2333 participants. Factors associated with N. americanus infection included age group, male sex (adjusted odds ratio (aOR) 3.1, 95% confidence interval (CI) 2.4–4.2), working as a farmer (aOR 1.7, 95% CI 1.2–2.4), and completing secondary school or higher (aOR 0.29, 95% CI 0.16–0.53). Risk factors for Ascaris spp. infection included age group, living in a dwelling with more than six people (aOR 1.6, 95% CI 1.1–2.3), having a tube well or borehole as the household water source (aOR 3.7, 95% CI 1.3–10.8), and using a latrine shared between households 6 months previously (aOR 2.3, 95% CI 1.2–4.3). Handwashing before eating was protective against infection with any soil-transmitted helminth (aOR 0.79, 95% CI 0.65–0.95). In the context of regular deworming, few water, sanitation and hygiene-related factors were associated with soil-transmitted helminth infections. Future research examining the role of water, sanitation and hygiene in soil-transmitted helminth transmission is required, particularly in low transmission settings after cessation of deworming. Identifying improved indicators for measuring water, sanitation and hygiene behaviours is also a key priority.