18. A Spatially Explicit Environmental Health Surveillance Framework for Tick-Borne Diseases

We demonstrate how applying a spatially explicit context to an existing environmental health surveillance framework is vital for more complete surveillance of disease, and for disease prevention and intervention strategies. To illustrate this framework, we present a case study that involves estimating the risk of human exposure to Lyme disease. The spatially explicit framework divides the surveillance process into three components: hazard surveillance, exposure surveillance, and outcome surveillance. The components are used both collectively and individually, to assess risk of exposure to infected ticks. By utilizing all surveillance components, we identify different areas of risk which would not have been identified otherwise. Hazard surveillance uses maximum entropy modeling and Geographically Weighted Regression analysis to create spatial models that predict the geographic distribution of ticks in Texas. Exposure surveillance uses GIS methods to estimate the risk of human exposures to infected ticks, resulting in a map that predicts the likelihood of human-tick interactions across Texas, using LandScan 2008™ population data. Lastly, outcome surveillance uses kernel density estimation-based methods to describe and analyze the spatial patterns of tick-borne diseases, which results in a continuous map that reflects disease rates based on population location. Data for this study was obtained from the Texas Department of Health Services and the University of North Texas Health Science Center. The data includes disease data on Lyme disease from 2004 to 2008, and the tick distribution estimates are based on field collections across Texas from 2004 to 2008.