RESEARCH Environmental Risk and Meningitis Epidemics in Africa Anna M. Molesworth,* Luis E. Cuevas,* Stephen J. Connor,* Andrew P. Morse,† and Madeleine C. Thomson* Epidemics of meningococcal meningitis occur in areas with particular environmental characteristics. We present evidence that the relationship between the environment and the location of these epidemics is quantifiable and pro- pose a model based on environmental variables to identify regions at risk for meningitis epidemics. These findings, which have substantial implications for directing surveil- lance activities and health policy, provide a basis for moni- toring the impact of climate variability and environmental change on epidemic occurrence in Africa. Ethe “meningitis belt” of Africa’s Sahel region has the pidemics of meningitis occur worldwide. However, greatest incidence of the disease, with large epidemics attributed to predominantly group A meningococci; the endemic levels found in this region would be considered epidemic elsewhere. Although factors predisposing popu- lations to meningitis epidemics are poorly understood, population susceptibility, introduction of new strains, poor living conditions, and concurrent infections have all been implicated. Epidemics occur throughout Africa in the dry season, coincide with periods of very low humidity and dusty conditions, and disappear with the onset of the rains, suggesting that these environmental factors may also play an important role in the occurrence of the disease (1–3). Lapeyssonnie (4) observed in 1963 that epidemics largely occurred in a semi-arid zone south from the Sahara, with 300–1,100 mm mean annual rainfall, and Chees- brough et al. (5) suggested in 1995 that areas that are humid throughout the year have low disease rates. In West Africa, Waddy (1958) described an area that suffered epi- demics as having “… only one definable frontier, the junc- tion of the forest…with the savanna…, when there is an abrupt change from a permanently humid climate to one with a severe dry season” (6). Epidemics have been rarely reported from the humid forested or coastal regions, even when neighboring areas are severely affected. *Liverpool School of Tropical Medicine, Liverpool, United Kingdom; and †University of Liverpool, Liverpool, United Kingdom The timing of future outbreaks is unpredictable; tools that identify the key environmental factors associated with areas prone to meningitis epidemics would help us to understand the basis for these outbreaks and eventually optimize prevention and control activities. We describe a model that predicts the probability, based on environmen- tal information, of an area experiencing an epidemic of meningitis. Methods Epidemiologic Data Details of all known meningitis epidemics occurring before 2000 in countries comprising continental Africa were compiled from information documented in the pub- lished literature and unpublished institutional reports at the end of June 2001. All epidemics reported in the medical literature were identified in PubMed’s online database of medical literature (United States National Library of Medicine, available from: URL: http://www.ncbi.nlm. nih.gov/PubMed/) through manual searches and by cross- referencing publications. We obtained unpublished infor- mation from Web searches or directly from international and national organizations involved in disease control and humanitarian aid (1). Epidemics reported at the provincial (second adminis- trative level) and district level were located by using administrative boundaries available from the U.S. Geological Survey EROS Data Centre Africa Data Dissemination Service, Sioux Falls, SD (available from: URL: http://edcintl.cr.usgs.gov/adds/). Locations of vil- lages or towns were verified by using the National Imagery and Mapping Agency’s GEONet gazetteer (available from: URL: http://www.nima.mil/), historical reference atlases and maps contained in the original reports, and were mapped to the current administrative boundaries by using ArcView 3.1 geographic information system (GIS) (ESRI, Redlands, CA). We assumed that events reported at the provincial level affected all constituent districts and excluded epidemics reported only at the national level. Emerging Infectious Diseases • Vol. 9, No. 10, October 2003 1287