Measuring malaria incidence

Why are disease burden estimates important? There are two sets of reasons: 1) technical, e.g. national priority setting etc and 2) political economy of health, e.g. advocacy and visibility, donor influence, etc. Thus, estimates are often quite contentious apart from the methodology used. The practical applications of burden estimation are on the other hand limited. Monitoring and evaluation systems can, with valid measurements of trend, help allocate regional resources, determine impact, and respond to outbreaks without necessarily measuring the magnitude of disease.

There are broadly two competing approaches for estimating malaria burden. One extrapolates from maps and surveys of population cross-sections, the other extrapolates from routinely collected surveillance data. Both have certain assumptions and biases: the former tends to overestimate, the latter generally underestimates. How should countries proceed? A new article from WHO in PloS Medicine (open access!) describes and contrasts each in a careful and informative way including actual results from 2009. While neither method is perfect, the authors present a compelling case for investing in surveillance-based approaches in the long run particularly outside of hyperendemic settings and in the context of intervention scale-up and declining transmission. Only that approach can improve the health system, and provide disaggregated and timely data amenable to frequent updates.

An accompanying editorial by Mueller, Slutsker, and Tanner broadly agrees with the author’s outlook though it includes a careful placative statement:

The two methods thus have their unique strengths and weaknesses, and rather than seeing them as competing approaches, they should be synergistically combined.

At first pass this seems a sensible assertion but on closer examination, and without other supporting text, it’s not clear what to make of it. Which distinct synergies do they envision? Should the two methods be used globally, i.e. one in countries without quality surveillance and the other elsewhere? Or should the two methods always be used in each nation? Why? Should they be used indefinitely – what about when surveillance systems mature? Are there not trade-offs both in time and space? Such discussion, drawing on the considerable program experience of the writers, would have been more helpful than conciliatory statements of questionable sincerity.

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