SPATIAL-ANALYSIS OF THE DISTRIBUTION OF LACROSSE ENCEPHALITIS IN ILLINOIS, USING A GEOGRAPHIC INFORMATION-SYSTEM AND LOCAL AND GLOBAL SPATIAL STATISTICS

The spatial and temporal distribution of LaCrosse encephalitis cases i n Illinois was analyzed using a geographic information system (GIS) an d spatial statistics. Case data were obtained from the Illinois Depart ment of Public Health and mapped on the county, town, and address leve l. Human cases were concentrated in and around the city of Peoria in c entral Illinois. Local spatial statistics were used to identify hot sp ots where cases appear to be concentrated in the Peoria region. Severa l small towns surrounding the city of Peoria appeared as foci where ca ses were most common. Second-order spatial analysis of the case distri bution was conducted on the address level. Cases were clustered within a range of 3.0 km in the city of Peoria. Since most cases appear to b e associated with residential (peridomestic) exposure, and since sever al cases have been reported from neighboring addresses, transmission m ay be concentrated around specific sites (hardwood ravines, tire piles ). The GIS and spatial analysis may be useful in identifying and targe ting for intervention potential sites of enzootic transmission.