Spillover effects of community wide deworming in Ethiopia

Study Context

Soil-transmitted helminth (STH) infections remain a pervasive public health issue in low- and middle-income countries, especially in Ethiopia, where over 79 million people are at risk. Left untreated, STH infections can cause anemia, malnutrition, impaired physical and cognitive development in children, and reduced productivity in adults. Although school-based mass drug administration (sMDA) has been the primary control strategy, its effectiveness in interrupting transmission has been limited due to rapid reinfection and the continued presence of untreated sources among preschool-aged children and adults, suggesting the need for community wide deworming approaches. However, little is known about its effectiveness and externalities.   

This study sought to evaluate the treatment & spillover effects  of a community-wide mass drug administration (cMDA) intervention compared to sMDA alone on STH prevalence and reinfection among children and caregivers.

Study Design

Using a double-randomized control trial design, the study included 1,155 primary households (578 treatment, 577 control) and 1,155 neighboring households in four districts of Jimma, Ethiopia to assess both direct and spillover effects. Data collection included stool samples from children and caregivers (analyzed using the Kato-Katz method), socio-demographic surveys, and qualitative interviews with 24 key informants. The trial was complemented by an ex-ante impact analysis to simulate effectiveness of various deworming scenarios and assess long-term effectiveness and cost-efficiency.

Results and Policy Lessons

Baseline data showed higher magnitudes of STH infections in both direct and their neighborhoods. Preliminary exante impact analysis results showed that annual community-wide cMDA significantly reduces STH prevalence in the short term, with greater declines among both direct and indirect recipients . However, reinfection remains a challenge without complementary interventions.  Biannual deworming combined with WASH  could also lead to the greatest long-term reductions in STH prevalence – albeit at a higher cost. Qualitative insights also revealed factors such as low access to and coverage of drugs, community resistances and non-compliance potential underestimate measures of externalities of  cMDA interventions. Future research aims to conduct the large scale field trial to estimate spillover effect under network interference and non compliance and also combine it with a realist evaluation approach.