Investigating Bias in School-Based Deworming Coverage Estimates from the DeWorm3 Trial

Background: Soil Transmitted Helminths (STH) infect over 1.5 billion people globally, causing anemia and growth stunting that result in an annual toll of 1.9 million Disability-Adjusted Life Years. School based deworming (SBD) via Mass Drug Administration (MDA) campaigns with albendazole or mebendazole has been recommended by the World Health Organization to reduce the prevalence of STH in endemic areas. The DeWorm3 Trial is a cluster randomized trial investigating the feasibility of interrupting the transmission of STH with community-wide MDA for three study sites in Benin, India, and Malawi.
Methodology/Principal Findings: This analysis examines data from the DeWorm3 Trial to quantify discrepancies between school-level reporting of SBD and gold-standard individual-level survey reporting of SBD available from the DeWorm3 Trial’s intervention arm. Population-weighted averages of school level SBD were calculated at the cluster level and compared to directly aggregated individual-level estimates of SBD to produce a Mean Squared Error (MSE) estimate for each study site. These MSE values were applied to SBD estimates from the control arm of the DeWorm3 Trial, where only school- level reporting of SBD had been collected, in order to project what coverages would have been for individual-level reporting of SBD.
In each site, SBD coverage was reported as being substantially higher in the school-level datasets than in the gold standard individual-level datasets, indicating that school-level SBD reporting may be overestimating SBD coverage. In Benin, average SBD coverage in the control arm dropped from 89.1% to 70.5% when applying observed MSE to project expected coverages. In India, the expected coverages decreased from 97.7% to 84.5%, and in Malawi, expected coverages decreased from 41.5% to 37.5%.
Conclusions/Significance: These estimates indicate that school-level reporting of SBD likely overestimate program reach and effectiveness. These findings suggest that current estimates of coverage derived from school-based program data may substantially overestimate true pediatric deworming coverage.