1. Public Health Group, KEMRI/Wellcome Trust Research Laboratories PO Box 43640, 00100 Nairobi, Kenya
2. Centre for Tropical Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK
3. TALA Research Group, Tinbergen Building, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
4. Faculty of Tropical Medicine, Mahidol University, Bangkok 10400, Thailand

Correspondence to: Robert W. Snow^1,2 Correspondence and requests for materials should be addressed to R.W.S. (Email: rsnow@wtnairobi.mimcom.net).

Abstract

Interest in mapping the global distribution of malaria is motivated by a need to define populations at risk for appropriate resource allocation^{1, 2} and to provide a robust framework for evaluating its global economic impact^{3, 4}. Comparison of older^{5, 6, 7} and more recent^{1, 4} malaria maps shows how the disease has been geographically restricted, but it remains entrenched in poor areas of the world with climates suitable for transmission. Here we provide an empirical approach to estimating the number of clinical events caused by Plasmodium falciparum worldwide, by using a combination of epidemiological, geographical and demographic data. We estimate that there were 515 (range 300–660) million episodes of clinical P. falciparum malaria in 2002. These global estimates are up to 50% higher than those reported by the World Health Organization (WHO) and 200% higher for areas outside Africa, reflecting the WHO's reliance upon passive national reporting for these countries. Without an informed understanding of the cartography of malaria risk, the global extent of clinical disease caused by P. falciparum will continue to be underestimated.

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