Spatial analysis of Lyme disease incidence in Howard County, Maryland

Background: In 2009, the Centers for Disease Control reported 38,468 confirmed and probable cases of Lyme disease in the United States. Lyme patients may suffer severe immediate symptoms, and some report long-term disability following the infection. This project characterized the geographic heterogeneity of Lyme disease in Howard County, Maryland, an area with historically high Lyme incidence. Methods: This project used geographic information systems (GIS) to aggregate and map Lyme cases reported to the Howard County Health Department, and Kulldorff's spatial scan statistic identified disease clusters in the study area. Results: The areas of highest incidence and relative risk were concentrated in the south-central region of the county. A significant cluster of higher than expected case counts encompassed the western half of Howard County (RR= 1.70; p=0.000016). A significant cluster of lower than expected case counts was identified in the southeast area of the county (RR= 0.34; p=0.0000050). Discussion: This project produced multiple maps to identify spatial trends of Lyme disease and to pinpoint the areas of highest risk in Howard County. Overlaying these maps with maps of the built and natural environment allowed us to visualize correlations between Lyme disease incidence, cluster patterns, and environmental factors. Public policy leaders at the Howard County Health Department, the Maryland Department of Health and Mental Hygiene, and other governmental agencies may use these maps to guide intervention efforts to reduce the impact of the disease in the area.