Water, Sanitation and Hygiene (WASH) and environmental risk factors for soil-transmitted helminth intensity of infection in Timor-Leste, using real time PCR

No investigations have been undertaken of risk factors for intensity of soil-transmitted helminth (STH) infection in Timor-Leste. We present the first analysis of combined water sanitation and hygiene (WASH), environmental, ansocioeconomic risk factors undertaken using intensity of infection classes developed from qPCR diagnosis of STH. Questionnaires were used to collect WASH and demographic data from 24 villages in Manufahi District, Timor-Leste. An algorithm was developed to correlate PCR cycle threshold values to eggs per gram of faeces equivalents, using seeding experiments. Open-access environmental variables were obtained. A socioeconomic quintile was developed using principal component
analysis. Multinomial mixed-effects regression was used to assess risk factors for intensity of Necator americanus and Ascaris infection in 2152 participants. In adjusted models incorporating WASH, socioeconomic and environmental variables, environmental variables were generally associated with infection intensity for both N. americanus and Ascaris spp. Precipitation (in centimetres) was associated with increased risk of moderate-intensity (adjusted relative risk (ARR) 6.1; 95% confidence interval (CI) 1.9-19.3) and heavy-intensity (ARR 6.6; 95%CI 3.1-14.1) N. americanus infection, as was sandy-loam soil around household (moderate-intensity ARR 2.1; 95%CI 1.0-4.3; heavy-intensity ARR 2.7; 95%CI 1.6-4.5; compared to no infection). For Ascaris, alkaline soil around the household was associated with reduced risk of moderate-intensity infection (ARR 0.21; 95%CI 0.09-0.51), and heavy-intensity infection (ARR 0.04; 95%CI 0.01-0.25). Few WASH risk factors were significant. Our novel approach of assigning infection intensity classes to PCR-diagnosed STH infection requires further research. In this high-prevalence setting, significant risk associations with environmental factors suggest that anthelmintic treatment should be integrated with other interventions, as conditions are favourable for ongoing environmental transmission. Integrated STH control strategies should be explored as a priority.