Ecoepidemiology of tularemia in the southcentral United States.

We combined county-based data for tularemia incidence from 1990 to 2003 for a nine-state region (Arkansas, Illinois, Indiana, Kansas, Kentucky, Missouri, Nebraska, Oklahoma, and Tennessee) in the southcentral United States with Geographic Information System (GIS)-based environmental data to determine associations between coverage by different habitats (especially dry forest representing suitable tick habitat) and tularemia incidence. High-risk counties (> 1 case per 100,000 person-years) clustered in Arkansas-Missouri and far eastern Oklahoma and Kansas. County tularemia incidence was positively associated with coverage by dry forested habitat suitable for vector ticks for Oklahoma-Kansas-Nebraska and Arkansas-Missouri but not for Illinois-Indiana-Kentucky-Tennessee. A multivariate logistic regression model predicting presence of areas with risk of tularemia based on GIS-derived environmental data was developed for the Arkansas-Missouri tularemia focus. The study shows the potential for research on tularemia ecoepidemiology and highlights the need for further modeling efforts based on acarologic data and more fine-scale point or zip code/census tract epidemiologic data.