A micro-epidemiological analysis of febrile malaria in Coastal Kenya showing hotspots within hotspots.

Philip Bejon,Thomas N Williams,Christopher Nyundo,Bryan Greenhouse,Evasius Bauni,Mark Otiende,Judy Peshu,Simon I Hay,Teun Bousema,Steffen Borrmann,David Benz,Kevin Marsh,Peter W Gething,Mahfudh Bashraheil,David L Smith

doi:10.7554/elife.02130

Abstract

Malaria transmission is spatially heterogeneous. This reduces the efficacy of control strategies, but focusing control strategies on clusters or 'hotspots' of transmission may be highly effective. Among 1500 homesteads in coastal Kenya we calculated (a) the fraction of febrile children with positive malaria smears per homestead, and (b) the mean age of children with malaria per homestead. These two measures were inversely correlated, indicating that children in homesteads at higher transmission acquire immunity more rapidly. This inverse correlation increased gradually with increasing spatial scale of analysis, and hotspots of febrile malaria were identified at every scale. We found hotspots within hotspots, down to the level of an individual homestead. Febrile malaria hotspots were temporally unstable, but 4 km radius hotspots could be targeted for 1 month following 1 month periods of surveillance.DOI: http://dx.doi.org/10.7554/eLife.02130.001.

Highlights

The transmission of infectious disease often shows substantial heterogeneity (Woolhouse et al, 1997)
Stable spatial heterogeneity would be expected to lead to spatial heterogeneity in the acquisition of immunity, which may be evidenced by variation in the age profiles of children with febrile malaria
We found that malaria cases were spatially heterogeneous in an 8-km radius area of coastal Kenya

Summary

Introduction

The transmission of infectious disease often shows substantial heterogeneity (Woolhouse et al, 1997). Malaria transmission is determined by mosquito ecology and behavior, which is in turn determined by rainfall, hydrology, soils, human behavior and population distributions, and a range of other social, biotic and abiotic factors. Heterogeneity of malaria transmission is apparent at global scale (Gething et al, 2011), regional scale (Kleinschmidt et al, 2001a; Noor et al, 2009), and at fine scale in, for instance, Mali (Gaudart et al, 2006), Ghana (Kreuels et al, 2008), Ethiopia (Yeshiwondim et al, 2009) Kenya (Brooker et al, 2004; Ernst et al, 2006; Bejon et al, 2010), and Tanzania (Bousema et al, 2010).

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Conclusion