Distribution and treatment needs of soil-transmitted helminthiasis in Bangladesh: A Bayesian geostatistical analysis of 2017-2020 national survey data

Background: In Bangladesh, preventive chemotherapy targeting soil-transmitted helminth (STH) infections in school-age children has been implemented since 2008. To evaluate the success of this strategy, surveys were conducted between 2017 and 2020 in 10 out of 64 districts. We estimate the geographic distribution of STH infections by species at high spatial resolution, identify risk factors, and estimate treatment needs at different population subgroups. Methodology: Bayesian geostatistical models were fitted to prevalence data of each STH species. Climatic, environmental, and socioeconomic predictors were extracted from satellite images, open-access, model-based databases, and demographic household surveys, and used to predict the prevalence of infection over a gridded surface at 1 x 1 km spatial resolution across the country, via Bayesian kriging. These estimates were combined with gridded population data to estimate the number of required treatments for different risk groups. Principal findings: The population-adjusted prevalence of Ascaris lumbricoides, Trichuris trichiura, and hookworm across all ages is estimated at 9.9% (95% Bayesian credible interval: 8.0-13.0%), 4.3% (3.0-7.3%), and 0.6% (0.4-0.9%), respectively. There were 24 out of 64 districts with an estimated population-adjusted STH infection prevalence above 20%. The proportion of households with improved sanitation showed a statistically important, protective association for both, A. lumbricoides and T. trichiura prevalence. Precipitation in the driest month of the year was negatively associated with A. lumbricoides prevalence. High organic carbon concentration in the soil’s fine earth fraction was related to a high hookworm prevalence. Furthermore, we estimated that 30.5 (27.2; 36.0) million dosages of anthelmintic treatments for school-age children were required per year in Bangladesh. Conclusions/significance: For each of the STH species, the prevalence was reduced by at least 80% since treatment was scaled up more than a decade ago. The current number of deworming dosages could be reduced by up to 61% if the treatment strategy was adapted to the local prevalence. Author summary: Bangladesh was in 2003 one of the world’s countries that was most affected by soil-transmitted helminthiasis, an infection of parasitic intestinal worms, with prevalence estimates as high as 55%. Following recommendations put forth by the World Health Organization (WHO), Bangladesh initiated a national deworming program based on school mass drug administration at six-month intervals, which started in 2008. Data collected between 2017 and 2020 showed that this program has lead to a striking decrease in prevalence, which was now between 10.5% and 1% depending on the species. Entering a close to elimination setting, the disease’s control strategy can be refined according to local endemicity to reduce overtreatment. To inform such a shift, we predict the prevalence across Bangladesh at high spatial resolution and highlight zones of different endemicity. We also show the potential reduction of overtreatment and financial resources that could be achieved by treating according to WHO recommendations at the predicted endemicity levels.