Reactive Malaria Case Detection – Tools for Elimination

Kelly M. Searle, ScM and her advisor at the Johns Hopkins Bloomberg School of Public Health, William J. Moss, MD MPH share the findings from her masters thesis: “Evaluation of Reactive Case Finding to Target Focal Malaria Transmission in Two Different Settings in Macha, Zambia.” They offer ideas on how we can move toward the challenging target of malaria elimination…

figure-1-rdt-zambia-sm.jpgWith malaria elimination in the minds of many, new methods of identifying and treating asymptomatic parasite carriers are being investigated. The current study evaluated reactive case detection as a malaria transmission intervention. Reactive case detection is the result of a malaria case being identified in a clinic by passive case detection, testing and treating that individual and their household contacts, and surrounding neighbors.

Survey sample data from different areas of Macha, Zambia in 2007 and 2008 were used to determine proportions of malaria infected individuals caught passively and reactively. Simulations were done to extrapolate this data to non-sampled households. Radii surrounding identified positive households (index households) were examined to determine the proportion of positive households in each radius.

In the 2007 transmission setting, screening 500 meters surrounding index households would have identified 89% of all households with an RDT positive resident and 90% of all RDT positive individuals. Screening 1 kilometer surrounding index households would have identified 95% of all households with an RDT positive resident and 94% of all RDT positive individuals (Figure 1). In the 2008 transmission setting, screening 500-meters surrounding index households would have identified 77% of all households with an RDT positive resident and 76% of all RDT positive individuals. Screening 1 kilometer surrounding index households would have identified 89% of all households with an RDT positive resident and 89% of all RDT positive individuals (Figure 2).

figure-2-rdt-zambia-sm.jpgReactive case detection has the potential to be an effective malaria intervention for populations of both moderate transmission settings and transmission settings transitioning (or that have recently transitioned) from moderate to low. With reactive case detection, a large proportion of malaria-infected individuals are accounted for using screening radius of 500 meters. A greater proportion of total households would have to be screened in the lower transmission setting, likely due to the overall lower numbers of cases existing. For reactive case finding to be most effective, it should be targeted at malaria foci and hotspots where transmission is greater than the overall area.

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