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 infec-
tion during the 2003 outbreak. After we adjusted for identi-
fied 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 out-
doors during prime mosquito-biting hours than Fort Collins
residents. Personal protective practices may directly influ-
ence rates of WNV infection and remain important even
when comprehensive community mosquito control meas-
ures are implemented.
(WNV)–affected areas is to practice the 4 Ds of preven-
tion: 1) DEET (N,N-diethyl-m-toluamide): wear an insect
repellent containing DEET; 2) dress: wear long sleeves and
long pants; 3) drain: drain standing water around the home;
and 4) dusk to dawn: limit time outdoors during this time.
Although the 4 Ds have been used by many state and local
health departments to promote personal prevention, the
question remains, how well do these tactics work to pre-
In 2003, ≈30% (2,947) of human WNV cases in the
United States were reported in Colorado. Among infected
n the United States, the mantra familiar to public health
workers and residents living in West Nile virus
residents, 63 died (1). WNV transmission was especially
intense in northern Colorado, including Larimer County.
Among county residents, 546 laboratory-confirmed cases
of WNV disease, including 63 neuroinvasive disease cases
and 9 deaths (2), occurred. Officials at the Larimer County
Department of Health and Environment noted differences
in age-adjusted rates of WNV neuroinvasive disease
between the 2 largest cities in the county. WNV neuroinva-
sive disease rates were used because neuroinvasive cases
are more likely to be captured in surveillance systems
because of illness severity, which often requires hospital-
ization and prompt laboratory diagnosis, unlike the gener-
ally milder West Nile fever. Furthermore, WNV
neuroinvasive disease cases are typically used to draw
comparisons between geographic areas and assess rates
over time (3,4). The city of Loveland had a much higher
age-adjusted rate of neuroinvasive disease (38.6/100,000)
than the city of Fort Collins (15.9/100,000); standardized
risk ratio 2.43 (95% confidence interval [CI] 1.21–4.87,
p<0.01). These findings were unexpected given the eco-
logic and demographic similarities of the 2 cities and a
long-term comprehensive mosquito control program in
Among the 265,489 Larimer County residents in July
2003, most lived in the cities of Fort Collins (125,461) and
Loveland (55,905) (5). Although some limited ecologic
differences exist (i.e., Loveland water surface area is ≈2.5×
greater), Fort Collins and Loveland are largely similar.
Demographically, both cities are ≈90% white with 9%
reported Hispanic ethnicity, 8%–13% of the residents are
≥65 years of age, and the annual household estimated
median income is ≈$45,000 per year (5).
Loveland and Fort Collins are both situated in a high
plains ecologic zone. The dominant WNV vector mosqui-
to species are Culex tarsalis and Cx. pipiens (6). During
the 2003 outbreak, ≈20–40 mosquito traps were collected
Behavioral Risks for West Nile V irus
Disease, Northern Colorado, 2003
Indira B. Gujral,* Emily C. Zielinski-Gutierrez,† Adrienne LeBailly,* and Roger Nasci†
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 3, March 2007419
*Larimer County Department of Health and Environment, Fort
Collins, Colorado, USA; and †Centers for Disease Control and
Prevention, Fort Collins, Colorado, USA
2. Colorado Department of Public Health and Environment. Human
West Nile virus infections: Colorado, 2005 [cited 2006 Dec 26].
Available from http://www.cdphe.state.co.us/dc/zoonosis/wnv/
3. Centers for Disease Control and Prevention. Epidemic/epizootic
West Nile virus in the United States: guidelines for surveillance,
prevention, and control. Atlanta: The Centers; 2003. p. 18–20.
4. Centers for Disease Control and Prevention. West Nile virus activi-
ty—United States, January 1–December 1, 2005. MMWR Morb
Mortal Wkly Rep. 2005;54:1253–6.
5. United States Census Bureau. State and county quickfacts. Fort
Collins (CO): United States Census Bureau; 2005.
6. Hayes EB, Komar N, Nasci RS, Montgomery SP, O’Leary DR,
Campbell GL. Epidemiology and transmission dynamics of West
Nile virus disease. Emerg Infect Dis. 2005;11:1167–73.
7. Mississippi Department of Health. West Nile virus. Jackson (MS):
The Department; 2006.
8. Slavinski S, Jones E. Evaluation of the Mississippi fight the bite
campaign. CDC Fifth National Conference on West Nile Virus in
the United States. Feb 3–5, 2004. Atlanta: Centers for Disease
Control and Prevention; 2004.
9. Hosmer DW, Lemeshow S. Applied logistic regression. 2nd ed.
New York: Wiley-Interscience; 2000.
10. Benson, Purnell H. How many scale categories shall we use in con-
sumer research? Journal of Marketing. 1970;35:59–61.
11. Mostashari F, Bunning ML, Kitsutani PT, Singer DA, Nash D,
Cooper MJ, et al. Epidemic West Nile encephalitis, New York,
1999: results of a household-based seroepidemiological survey.
12. Blendon R. Residents of states reporting most West Nile virus cases
are less likely to take precautions against mosquitoes. Press
Release. Boston: Harvard School of Public Health; 2004.
13. McCarthy TA, Hadler JL, Julian K, Walsh SJ, Biggerstaff BJ,
Hinten SR, et al. West Nile virus serosurvey and assessment of per-
sonal prevention efforts in an area with intense epizootic activity:
Connecticut, 2000. Ann N YAcad Sci. 2001;951:307–16.
14. Conner M, Norman P. Predicting health behaviour: research and
practice with social cognition models. Philadelphia: Open
University Press; 1996.
15. Weinstein ND. Testing four competing theories of health-protective
behavior. Health Psychol. 1993;12:324–33.
16. Brewer NT, Weinstein ND, Cuite CL, Herrington JE. Risk percep-
tions and their relation to risk behavior. Ann Behav Med.
17. Zielinski-Gutierrez EC, Hayden MH. A model for defining West
Nile virus risk perception based on ecology and proximity.
Address for correspondence: Indira B. Gujral, 1415 Crestmore Pl, Fort
Collins, CO 80521, USA; email: firstname.lastname@example.org
Behavioral Risks for West Nile Virus Disease
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 3, March 2007 425