Negligible impact of mass screening and treatment on meso-endemic malaria transmission at West Timor in Eastern Indonesia: a cluster-randomised trial

Background. Mass screening and treatment (MST) aims to reduce malaria risk in communities by identifying and treating infected without regard to illness. Methods. A cluster-randomized trial evaluated malaria incidence with and without MST. Clusters were randomized to three, two, or no MST interventions: MST3=6 clusters (156 households/670 individuals); MST2=5 clusters (89 households/423 individuals); and MST0=5 clusters (174 households/777 individuals). All clusters completed the study with 15 residents withdrawing. A cohort of 324 school children (MST3 n=124; MST2 n=57; MST0 n=143) negative by microscopy at enrolment, evaluated the incidence density of malaria during 3mo MST and 3mo following. The MST intervention involved community-wide expert malaria microscopic screening and standard therapy with dihydroartemisinin-piperaquine and primaquine for G6PD-normal subjects (single 0.75 mg/kg dose for Plasmodium falciparum; 14 daily 0.25 mg/kg for P. vivax). All blood exams included PCR assays which did not guide on-site treatment. Results. The risk ratios for incidence density of microscopically patent malaria in MST3 or MST2 relative to that in MST0 clusters were 1.00 (95% CI 0.53 – 1.91) and 1.22 (95% CI 0.42 – 3.55), respectively. Similar results were obtained with molecular analysis on a school-aged cohort, and species-specific (P. falciparum and P. vivax) infections. Microscopically sub-patent, untreated infections accounted for 72% of those infected. Conclusions. Two or three rounds of MST within 3 months did not impact the force of anopheline mosquito-borne infection in these communities during or after the interventions. The high rate of untreated microscopically sub-patent infections likely explains the observed poor impact.