84 - DEVELOPING AND IMPLEMENTING A WEST NILE VIRUS DRIVEN RESPONSE GRID SYSTEM USING ARCGIS HOT-SPOT ANALYSIS IN ORANGE COUNTY, CA

Abstract: In the wake of Orange County’s (California) worst West Nile virus (WNV) epidemic in 2014, Orange County Mosquito and Vector Control District (OCMVCD) took steps to increase sensitivity of early detection of WNV virus activity and decrease control response time. In 2019, OCMVCD developed and implemented a Geospatial Response Identification System (GRIdS) derived from 15 years (2004 – 2018) of spatial data for WNV human cases and virus positive dead birds. Orange County Mosquito and Vector Control District used these spatial data to construct a hot-spot analysis, which identified three Countywide regions based on WNV risk: high, medium, and low. Each area was divided into blocks (one gravid trap per block) with dimensions set to accommodate OCMVCD’s ground-based adulticiding resources. Each block was further divided into smaller cells to delineate sections for additional weekly mosquito sampling that was activated upon an initial WNV detection. The area with the highest density of WNV activity, based on human cases and positive dead birds, was assigned a smaller surveillance grid compared to the medium and low risk areas. Mosquito trapping was relocated towards the centroid of each block. Within each risk area, the blocks established a standard unit for calculating infection rates based on routine and extended trapping efforts. During the first implementation year (2019) and subsequent years, the grid system enhanced communication of risk to constituents and stakeholders at a neighborhood level and allowed for a more rapid control response.