481. West Nile Outbreak in Dallas County, Texas, 2012
Session: Poster Abstract Session: Public Health
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
Background: Dallas County has experienced wide variations in the severity of seasonal WNV outbreaks over the past decade.  Although only 2 WNV cases were reported in 2010 and 2011, a record 398 cases occurred in Dallas County during the 2012 season. The unprecedented magnitude of this focal outbreak prompts ongoing assessments of surveillance data from prior WNV seasons, to discern epidemiologic commonalities in outbreak dynamics.

Methods: Case interviews and medical chart reviews were conducted for all WNV cases reported to the health department, and incidence rates calculated. Mosquito data from existing municipal and county seasonal WNV surveillance programs were used to calculate Culex quinquefasciatusinfection rates with a bias-corrected maximum likelihood estimation. Mosquito traps, WNV cases, and asymptomatic presumptive viremic blood donors (PVDs) were mapped in geographic information systems.

Results: From June through December 2012, 173 cases of West Nile Neuroinvasive Disease (WNND), 225 West Nile Fever (WNF), 17 asymptomatic PVDs, and 19 deaths were reported in Dallas County. Of the 216 hospitalized WNV cases, 31% (67) required ICU admission, and 27% (50) required discharge to long-term care or rehabilitation facilities. The WNND incidence rate was 7.05 per 100,000 in 2012, compared with 2.86 in the prior peak outbreak year of 2006.   Higher concentrations of cases were noted in the northeastern section of the County, where WNND incidence rates were 16.63 (2006: 4.89). In the 2012 and 2006 outbreaks, the first positive mosquito pools appeared earlier than in the non-outbreak seasons, with higher and earlier peak mosquito infection rates of 48.3 (95% CI=35.6, 65.8) per 1,000 female mosquitoes in 2012, and 58.0 (95% CI=25.2, 128.8) in 2006.  Peak mosquito infection rates preceded peak weeks of onset of WNND cases by 1-2 weeks. 

Conclusion: Significant morbidity occurred during the 2012 WNV outbreak in Dallas County, with similarities observed in environmental surveillance patterns with the 2006 WNV outbreak season, including early and rapid increases in mosquito infection rates.  The potential for large-scale focal WNV outbreaks underscores the need for maintenance of robust public health vector surveillance programs to guide public health control measures and resources.

Wendy M. Chung, MD, MSPH1, Sibeso N. Joyner, MPH1, Sonya M. Hughes, MPH1, Christen M. Buseman, PhD, MPH1, Elizabeth Smith, RN1, Taye Derse, MD, MPH1, James P. Luby, MD2 and Robert W. Haley, MD2, (1)Dallas County Department of Health and Human Services, Dallas, TX, (2)Epidemiology, University of Texas Southwestern Medical Center, Dallas, TX


W. M. Chung, None

S. N. Joyner, None

S. M. Hughes, None

C. M. Buseman, None

E. Smith, None

T. Derse, None

J. P. Luby, None

R. W. Haley, None

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