Social Science & Medicine 55 (2002) 1015–1024 The spatial epidemiology of cholera in an endemic area of Bangladesh Mohammad Ali a, *, Michael Emch b , J.P. Donnay c , Mohammad Yunus d , R.B. Sack e a International Vaccine Institute, Seoul, South Korea b Department of Geography, Portland State University, USA c Department of Geomatics, University of Liege, Belgium d ICDDR, B: Centre for Health and Population Research, Bangladesh e Johns Hopkins University, USA Abstract This paper defines high-risk areas of cholera based on environmental risk factors of the disease in an endemic area of Bangladesh. The risk factors include proximity to surface water, high population density, and low educational status, which were identified in an earlier study by the authors. Cholera data were analyzed by spatially referenced extended household units for two time periods, 1983–1987 and 1992–1996. These periods were chosen because they had different dominant cholera agents. From 1983–1987 classical cholera was dominant and from 1992–1996 El Tor was dominant. By defining high-risk areas based on risk factors, this study builds a spatial risk model for cholera. The model is then evaluated based on the locations of observed cholera cases. The study also identifies the determinants of death due to cholera for the two different time periods dominated by the different cholera agents. The modeled risk areas that were based on the risk factors were found to correspond with actual distributions of cholera morbidity and mortality. The high-risk areas of the dominant cholera agents are relatively stable over time. However, from 1983–1987 El Tor cholera, which was not the dominant agent during that period, was not associated with high-risk areas, suggesting that the El Tor habitat may have changed over time. The case fatality rate for cholera was related to proximity to a diarrhea treatment hospital in the study area. r 2002 Published by Elsevier Science Ltd. Keywords: Cholera; Disease risk; Spatial analysis; Bangladesh Introduction and Background An important part of health-needs assessment is the identification of high-risk areas for a disease because understanding the characteristics of high-risk areas may indicate what is needed to improve health care provision (Haining, 1996). However, most epidemiological studies overlook the spatial components of disease and focus solely on characteristics of the people who contract a disease (Smoyer, 1998). While these studies are useful for identifying biological factors of a disease, they usually cannot establish accurate individual exposure levels for the critical risk factors of the disease (Haining, 1998). The incorporation of spatial components in health studies facilitates the identification of high-risk disease areas, the identification of sources of disease, the definition of high-risk populations, and the optimal allocation of health facilities (Jacquez, 2000). Identifying high- and low-risk areas can help with the estimation of resources needed for effective health planning and it may help determine the underlying processes responsible for the spatial patterns of disease. Methods for identifying high-risk areas by disease clustering techniques are well established (Myaux, Ali, Chakraborty, & de Francisco, 1997a; Kulldorff & Nagarwalla, 1995; Besag & Newell, 1991). However, *Corresponding author. International Vaccine Institute, Kwanak PO Box 14, Seoul, South Korea 1S1-600. E-mail address: mali@ivi.int (M. Ali). 0277-9536/02/$ - see front matter r 2002 Published by Elsevier Science Ltd. PII:S0277-9536(01)00230-1