Identification of hyperendemic foci of horses with West Nile virus disease in Texas.

OBJECTIVE To determine whether West Nile virus (WNV) disease hyperendemic foci (hot spots) exist within the horse population in Texas and, if detected, to identify the locations. SAMPLE POPULATION Reports of 1,907 horses with WNV disease in Texas from 2002 to 2004. PROCEDURES Case data with spatial information from WNV epidemics occurring in 2002 (1,377 horses), 2003 (396 horses), and 2004 (134 horses) were analyzed by use of the spatial scan statistic (Poisson model) and kriging of empirical Bayes smoothed county attack rates to determine locations of horses with WNV disease in which affected horses were consistently (in each of the 3 study years) clustered (hyperendemic foci, or hot spots). RESULTS 2 WNV hot spots in Texas, an area in northwestern Texas and an area in eastern Texas, were identified with the scan statistic. Risk maps of the WNV epidemics were qualitatively consistent with the hot spots identified. CONCLUSIONS AND CLINICAL RELEVANCE WNV hot spots existed within the horse population in Texas (2002 to 2004). Knowledge of disease hot spots allows disease control and prevention programs to be made more efficient through targeted surveillance and education.