Cost-effectiveness of mass drug administration with ivermectin against strongyloidiasis: a modelling study

Abstract

Background: Strongyloidiasis, caused by the parasitic intestinal worm Strongyloides stercoralis, infects hundreds of millions of people globally. Current school-based preventive chemotherapy (PC) programs that use benzimidazole derivatives (e.g., albendazole) against soil-transmitted helminths do not effectively treat strongyloidiasis, which requires treatment with ivermectin. We estimate the cost-effectiveness of mass drug administration with ivermectin for the control of strongyloidiasis. Methods: We developed a mathematical model to simulate the population dynamics of S. stercoralis and the impact of school-based and community-wide PC across a range of epidemiological settings. We simulated 10-year PC programs with varying treatment coverages. We estimated a primary outcome of disability-adjusted life years (DALYs) averted by each PC strategy and calculate the programmatic cost (US$) of each strategy. We estimated cost-effectiveness by comparing strategies by their incremental cost-effectiveness ratios (US$/averted DALY) and expected loss curves. Findings: The model found community-based PC was the most cost-effective strategy (≤600 US$ / DALY averted), despite costing approximately 5 times as much as school-based PC. Community-based PC targeted at ages 5 and above reduced infection levels close to 0% within 5 to 6 years. School-based PC was predicted to have very little impact. These results were robust across a range of epidemiologic settings above a measured prevalence of 2-5% in school age children. Interpretation: Annual community-based PC is the most cost-effective public health strategy to control strongyloidiasis, being superior to school-based PC due to most of the infections and mortality occurring in adults. A baseline prevalence of 2% of infection in school age children, as measured by Baermann or stool culture, is a suitable minimum threshold for cost-effective implementation of community-based PC. Funding: World Health Organization.