Yard Flooding by Irrigation Canals Increased the Risk of West Nile Disease in El Paso, Texas

PURPOSE: To investigate the effects of use of water from irrigation canals to flood residential yards on the risk of West Nile disease in El Paso, Texas. METHODS: West Nile disease confirmed cases in 2009 through 2010 were compared with a random sample of 50 residents of the county according to access to and use of water from irrigation canals by subjects or their neighbors, as well as geo-referenced closest distance between their home address and the nearest irrigation canal. A windshield survey of 600 m around the study subjects' home address recorded the presence of irrigation canals. The distance from the residence of 182 confirmed cases of West Nile disease reported in 2003 through 2010 to canals was compared with that of the centroids of 182 blocks selected at random. RESULTS: Cases were more likely than controls to report their neighbors flooded their yards with water from canals. Irrigation canals were more often observed in neighborhoods of cases than of controls. Using the set of addresses of 182 confirmed cases and 182 hypothetical controls the authors found a significant, inverse relation with risk of West Nile disease. CONCLUSIONS: Flooding of yards with water from canals increased the risk of West Nile disease. Ann Epidemiol 2011;21:922-929. (C) 2011 Elsevier Inc. All rights reserved.