The global distribution of clinical episodes of Plasmodium falciparum malaria

Abstract

A new ‘malaria map’ suggests that the disease is far more common than was thought. There is still no reliable estimate of the global distribution of the public health burden posed by malaria, making it impossible to allocate resources for malaria control on the basis of objective evidence. Snow et al. set out to improve the situation by developing a map of the global distribution of clinical episodes of Plasmodium falciparum malaria incorporating epidemiological, geographic and demographic data. The bottom line is a total of around 500 million cases in 2002, which is 50% higher than the WHO figure. For areas outside Africa the new estimate is twice the WHO figure, reflecting lax reporting procedures in some countries. Interest in mapping the global distribution of malaria is motivated by a need to define populations at risk for appropriate resource allocation1,2 and to provide a robust framework for evaluating its global economic impact3,4. Comparison of older5,6,7 and more recent1,4 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.