Geospatial risk prediction for hookworm infection and strongyloidiasis in adults, Dak Lak province, Vietnam

Despite a long-running soil-transmitted helminth (STH) control programme for school-aged children in Dak Lak province, Vietnam, STHs remain a persistent public health challenge, likely in part because adults are a reservoir that sustain parasite transmission. Additionally, previous studies showed high prevalence of Strongyloides stercoralis among adults in the province, with no MDA programme targeting this species. Here, we developed geospatial risk prediction models for hookworm and Strongyloides infection in adults to inform targeted interventions. Parasitological data for hookworm and Strongyloides species were obtained from two community-based studies conducted in Dak Lak province in 2020 and 2021, using quantitative polymerase chain reaction (qPCR) as the diagnostic tool. This data, together with open-source environmental and climatic data, was used to develop predictive models for hookworm and Strongyloides infection risk in adults using generalised linear mixed models. Residual spatial autocorrelation was assessed using semivariograms, and if present, a Matern’s covariance was incorporated in the model. Maps were then created to visualise the distribution of predicted infection risk across the province. Parasitological data were obtained from 708 adults (age ≥ 15 years) across 7 communities. Overall hookworm prevalence was 62.1% (community range 33.3–75.0%) and Strongyloides prevalence 10.7% (range 1.7–21.4%). Risk prediction maps identified higher-risk areas for hookworm infection throughout central and southern parts of the province, which were replicated in predictive models for moderate-and-heavy intensity hookworm infection risk. Predicted Strongyloides hotspots were found in northwestern and eastern areas. Our geospatial risk prediction maps for hookworm and Strongyloides revealed different higher-risk areas for each species. This informs the need for geographically targeted control strategies beyond current school-based interventions that address adult reservoirs of STH species and include ivermectin, as well as the inclusion of adults in monitoring and evaluation activities.