This paper examines the relationship between indoor residual spray (IRS) and malaria parasite infection in Gash Barka Zone, Eritrea, an area with near universal coverage of insecticide treated bednets (ITN) and already low malaria parasite prevalence. A community randomized control trial was conducted in 2009. Malaria parasite infection prevalence was 0.5% [95% confidence interval (CI): 0.37-0.78%], with no significant difference detected between treatment and control areas. ITN possession remains high, with over 70% of households reporting ITN ownership [95% CI: 68.4-72.9]. ITN use among individuals within ITN-owning households was just under half [46.7% (95% CI: 45.4-48.0)]. Slight differences in ITN possession and use were detected between treatment and control areas. There was no significant difference in malaria parasite infection prevalence among individuals in households with ≥1 ITN compared to those in households without ITNs, nor among individuals reporting ITN use. Among individuals in ITN-owning households, sleeping under an ITN offered no statistically significant protection from malaria parasite infection. Community participation in environmental and larval habitat management activities was low: 17.9% (95% CI: 16.0-19.7). It is likely that IRS, larval habitat management and ITN distribution alone may be insufficient to interrupt transmission without corresponding high ITN use, sustained IRS application in areas where infections are clustered, and promptly seeking laboratory diagnosis and treatment of all fevers. Eritrea is ready for elimination, irrespective of inconclusive impact evaluation results.
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