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Malaria case investigation and reactive case detection (RACD) activities are widely implemented in low transmission settings to identify additional malaria infections and gather surveillance information, but with varying degrees of success. Challenges in conducting RACD include poor diagnostic sensitivity (particularly for low density and asymptomatic infections), knowledge gaps among those conducting RACD, financial and resource constraints, and operational and logistical difficulties. To improve infection detection and better target individuals at highest risk for infection, RACD strategies need to be evaluated and optimized to provide quality and nuanced surveillance information.

To support more effective surveillance and response strategies, this PhD project focused on evaluating RACD strategies to improve and optimize malaria surveillance in low transmission settings in the Asia Pacific region. Using a standardized monitoring and evaluation (M&E) tool, case investigation and RACD indicators were assessed, including the knowledge and practices of the staff conducting RACD. This PhD project explored the utility of molecular diagnostics and genotyping and targeted sociobehavorial RACD strategies for increasing infection detection and to understand the relatedness of infections identified during RACD. Also, the acceptability and feasibility of a presumptive treatment-based strategy to reduce malaria (referred to as reactive drug administration (RDA)) was evaluated.

Results revealed gaps in case investigation and RACD reporting completeness and timeliness and that staff were not always equipped with the appropriate documentation or have accurate knowledge on how to conduct RACD. Molecular diagnostics used in RACD in Thailand identified an additional 12 (0.6%) infections compared to no RACD-identified infections detected by microscopy. Of the four confirmed infections, only one (25%) was genetically related to the index case. In Indonesia, a sociobehavorial RACD strategy targeting high risk populations and work venues was able to identify 180 individuals for RACD yielding 8 infections compared to only one infection during household-based RACD. Shared risk factors between sociobehavorial RACD individuals and index patients include being male, 30-45 years of age, and occupation of logging or mining. In Thailand, an RDA strategy targeting within and around the household and forest-going co-workers was found to be acceptable by those that participated and feasible to be implemented by the malaria staff.

The quality of malaria case investigation and RACD activities and the knowledge of those implementing it can be improved using a standardized M&E tool. The molecular and genotyping findings may be useful for malaria programs in low transmission settings to increase infection detection in persistent malaria foci or among high-risk populations and to characterize local transmission patterns. When the highest risk individuals for malaria can be identified, a strategy like RDA may be useful to target and eliminate malaria to accelerate elimination efforts.