Behavioral Risks for West Nile Virus Disease, Northern Colorado, 2003

In 2003, residents in 2 adjacent cities in northern Colorado (Loveland and Fort Collins) had severe outbreaks of human West Nile virus (WNV) disease. Unexpectedly, age-adjusted neuroinvasive disease rates were higher in Loveland (38.6 vs. 15.9 per 100,000), which had a more extensive mosquito control program and fewer mosquitoes. A survey was conducted to assess differences in personal protection and risk practices by each city's residents. During May and June 2004, a random-digit dial telephone survey was conducted among adults to assess personal protection behavioral practices used to prevent WNV infection during the 2003 outbreak. After we adjusted for identified risk factors, Loveland residents were 39% more likely to report seldom or never using N,N-diethyl-m-toluamide (DEET), and ≈30% were more likely to report being outdoors during prime mosquito-biting hours than Fort Collins residents. Personal protective practices may directly influence rates of WNV infection and remain important even when comprehensive community mosquito control measures are implemented.