Preliminary investigation of the impact of mass drug administration on malaria transmission in Zanzibar.

Abstract

Abstract Background. Mass drug administration (MDA) is the simultaneous treatment of a defined population without diagnostic testing, irrespective of the presence of symptoms. MDA has been suggested as a malaria elimination strategy since today’s diagnostic tools are insufficiently sensitive to detect the low-density, asymptomatic infections thought to fuel remaining malaria transmission in low-endemic settings. A cluster-randomized controlled trial (CRCT) assessing MDA on Zanzibar was initiated in April 2016. This report investigates the impact MDA had on malaria transmission during 16 months follow-up. Methods. Eight areas received two rounds of MDA including dihydroartemisinin-piperaquine + single low dose primaquine (0.25 mg/kg) and were compared to eight similar control areas. Data on recorded clinical malaria cases detected at health facilities during the follow-up period was collected through Zanzibar’s malaria surveillance-system. Cumulative incidence and crude risk ratios were used to describe observed trends in malaria transmission. Results. During 16 months follow-up MDA fails to achieve a statistically significant lower risk of malaria in the intervention arm compared to the control arm; RR=0.85 (95% CI 0.69-1.03; P=0.10). No risk reduction was observed during the high transmission season immediately after MDA; RR=1.16 (95% CI 0.76-1.75; P=0.49). During the following year’s (2017) high transmission season the RR was 0.68 (95% CI 0.52-0.88; P=0.004). Discussion. Previous studies have concluded that MDA has a rapid effect on malaria transmission and that the difficulty is to maintain this effect. No such direct effect could be observed in this report. The reason for the observed reduced malaria risk during the high transmission season of 2017, one year after MDA was conducted, is unclear. Further analyses are needed to confirm the effectiveness MDA had on transmission.