Seasonality and survival associated with three outbreak seasons of West Nile virus disease in Oklahoma--2003, 2007, and 2012

West Nile virus (WNV) activity has fluctuated in the south-central United States since its introduction. Seasonal outbreaks are common, with three in Oklahoma during 2003, 2007, and 2012. Morbidity and mortality rates vary during each outbreak. Long-term neurologic sequelae in association with West Nile virus disease (WNVD) are well-described, but limited information is available about delayed mortality among acute WNV infection survivors. A retrospective cohort analysis of all confirmed and probable WNVD cases reported to the Oklahoma State Department of Health (OSDH) during 2003, 2007, and 2012 was performed. OSDH surveillance data and mortality data from Oklahoma's vital statistics database were used to construct a descriptive epidemiologic analysis of the geography, temporality, severity, and associated mortality for each outbreak season. A Kaplan-Meier survival curve and standardized mortality ratios (SMRs) were calculated to measure survival of the 2003 and 2007 WNVD cohorts. Seventy-nine cases during 2003, 107 cases during 2007, and 180 cases during 2012 met inclusion criteria. Median ages of the 2003, 2007, and 2012 cohorts were 48, 58, and 59 years, respectively; race, sex, and symptom information were not substantially different. Each outbreak season had a different severity, temporality, and geography. Age- and sex-adjusted SMRs for the combined 2003 and 2007 cohorts censored at 5 years was 0.9 (95% confidence interval 0.51-1.75); no substantial difference was observed between the survival curves. Although similar patterns of long-term mortality were evident on the survival curves, SMRs did not demonstrate increased 5-year cumulative risk for death for patients surviving acute WNV infection.