West Nile Virus, Texas, USA, 2012

Kristy O. Murray

, Duke Ruktanonchai, Dawn Hesalroad, Eric Fonken, and Melissa S. Nolan

Author affiliations: Baylor College of Medicine, Houston, Texas, USA (K.O. Murray,, M.S. Nolan); Texas Children’s Hospital, Houston (K.O. Murray, M.S. Nolan); Texas Department of State Health Services, Austin, Texas, USA (D. Ruktanonchai, D. Hesalroad, E. Fonken)

Abstract

During the 2012 West Nile virus outbreak in Texas, USA, 1,868 cases were reported. Male patients, persons > 65 years of age, and minorities were at highest risk for neuroinvasive disease. Fifty-three percent of counties reported a case; 48% of case-patients resided in 4 counties around Dallas/Fort Worth. The economic cost was > $47.6 million.

West Nile virus (WNV) first emerged in Texas, USA, in 2002 (1). Since then, the virus has become endemic, with ≈2,200 human cases reported in the state during 2002–2011 (2). In 2012, an unprecedented outbreak of WNV occurred in Texas; ≈1,900 cases were reported. The objective of this study was to understand the epidemiology of the 2012 WNV outbreak in Texas.

The Study

WNV infection is a reportable condition in Texas, with clinical cases passively reported by physicians to the local health departments, which in turn report to Texas Department of State Health Services (TxDSHS). We examined surveillance data for all reported cases for which symptom onset occurred during the 2012 calendar year, and we used descriptive statistics to describe the clinical features and demographic characteristics of reported case-patients. We calculated attack rates by sex, age, and race/ethnicity and incidence rates by county using population estimates for 2012 (3). Odds ratios (ORs), 95% CIs, and p values were calculated to determine differences in demographic variables between severe disease (WNV neuroinvasive disease [WNND], which included encephalitis, meningoencephalitis, and meningitis) and less severe disease (uncomplicated WNV fever). Epi Info 7.0 software (Centers for Disease Control and Prevention, Atlanta, GA, USA) was used for all statistical calculations.