| Understanding the Spatial Clustering of Severe Acute Respiratory Syndrome (SARS) in Hong Kong P.C. Lai,1 C.M. Wong,2 A.J. Hedley,2 S.V. Lo,3 P.Y. Leung,4 J. Kong,5 and G.M. Leung2 1Department of Geography, and 2Department of Community Medicine, University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China; 3Health Welfare and Food Bureau and 4Department of Health, Hong Kong Special Administrative Region, People's Republic of China; 5Division of Health Informatics, Hong Kong Hospital Authority, Hong Kong Special Administrative Region, People's Republic of China Abstract
We applied cartographic and geostatistical methods in analyzing the patterns of disease spread during the 2003 severe acute respiratory syndrome (SARS) outbreak in Hong Kong using geographic information system (GIS) technology. We analyzed an integrated database that contained clinical and personal details on all 1,755 patients confirmed to have SARS from 15 February to 22 June 2003. Elementary mapping of disease occurrences in space and time simultaneously revealed the geographic extent of spread throughout the territory. Statistical surfaces created by the kernel method confirmed that SARS cases were highly clustered and identified distinct disease "hot spots." Contextual analysis of mean and standard deviation of different density classes indicated that the period from day 1 (18 February) through day 16 (6 March) was the prodrome of the epidemic, whereas days 86 (15 May) to 106 (4 June) marked the declining phase of the outbreak. Origin-and-destination plots showed the directional bias and radius of spread of superspreading events. Integration of GIS technology into routine field epidemiologic surveillance can offer a real-time quantitative method for identifying and tracking the geospatial spread of infectious diseases, as our experience with SARS has demonstrated. Key words: geographic information systems, GIS, SARS, severe acute respiratory syndrome, spatial distribution. Environ Health Perspect 112:1550-1556 (2004) . doi:10.1289/ehp.7117 available via http://dx.doi.org/ [Online 27 July 2004]
Address correspondence to P.C. Lai, Department of Geography, University of Hong Kong, Pokfulam Rd., Hong Kong. Telephone: 852-2859-2830. Fax: 852-2559-8994. E-mail: pclai@hkucc.hku.hk We thank colleagues in the Department of Health and the Hong Kong Hospital Authority for data collection and processing, A. Mak and K. Chan for cartographic modeling and analyses, and P. Chau for data management. The Hui-Oi-Chow Trust Fund provided support for the development of the methodologic approach, and the Research Fund for the Control of Infectious Diseases sponsored work on infectious disease epidemiology at the University of Hong Kong. The authors declare they have no competing financial interests. Received 25 March 2004 ; accepted 27 July 2004. An erratum was published in Environ Health Perspect 113:A227 (2005) .
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