Malaria Treatment & Prevention
Measuring malaria incidence
How should we measure malaria burden? 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.
http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1001142
Some suggest both methods should be "should be synergistically combined". What do you think this means? 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?
Clive Shiff
This is an interesting and vexing problem because malaria is a fluctuating disease, the incidence rate varies with environmental characteristics. We like to think of it as static, but it not. There can be lots of cases at a pace during the rains, but few, if any during the dry season. After all the mosquito calls the shots here, and when they are not foraging, there is no transmission. The idea of the incidence (remember incidence is a rate, ie the number of cases/ total population over a defined period of time) as a measure is more accurate than the slide positive rate, because the latter is done as a crossectional analysis over a short period of time, so it is not really a rate, but a single measurement. So the level depends very much when it was done. Hence the question is difficult to answer.
I still feel that the broad classification of holo, hyper, meso and hypo endemic malaria is the best way to describe malaria, to try and be more precise requires a great deal in carefully collected data,
Clive Shiff
2:56 PM, 10 Jul 2012 | Permalink
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