Exploring water, sanitation, and hygiene coverage targets for reaching and sustaining trachoma elimination: G-computation analysis

BACKGROUND: Trachoma is the leading infectious cause of blindness. To reduce transmission, water, sanitation, and hygiene (WaSH) improvements are promoted through a comprehensive public health strategy. Evidence supporting the role of WaSH in trachoma elimination is mixed and it remains unknown what WaSH coverages are needed to effectively reduce transmission. METHODS/FINDINGS: We used g-computation to estimate the impact on the prevalence of trachomatous inflammation—follicular among children aged 1–9 years (TF(1-9)) when hypothetical WaSH interventions raised the minimum coverages from 5% to 100% for “nearby” face-washing water (<30 minutes roundtrip collection time) and adult latrine use in an evaluation unit (EU). For each scenario, we estimated the generalized prevalence difference as the TF(1-9) prevalence under the intervention scenarios minus the observed prevalence. Data from 574 cross-sectional surveys conducted in 16 African and Eastern Mediterranean countries were included. Surveys were conducted from 2015–2019 with support from the Global Trachoma Mapping Project and Tropical Data. When modeling interventions among EUs that had not yet met the TF(1-9) elimination target, increasing nearby face-washing water and latrine use coverages above 30% was generally associated with consistent decreases in TF(1-9). For nearby face-washing water, we estimated a ≥25% decrease in TF(1-9) at 65% coverage, with a plateau upon reaching 85% coverage. For latrine use, the estimated decrease in TF(1-9) accelerated from 80% coverage upward, with a ≥25% decrease in TF(1-9) by 85% coverage. Among EUs that had previously met the elimination target, results were inconclusive. CONCLUSIONS: Our results support Sustainable Development Goal 6 and provide insight into potential WaSH-related coverage targets for trachoma elimination. Targets can be tested in future trials to improve evidence-based WaSH guidance for trachoma.