title: Encephalitis hospitalization rates and inpatient mortality in the United States, 2000-2010.
abstract: BACKGROUND
  Encephalitis rates by etiology and acute-phase outcomes for encephalitis in the 21st century are largely unknown. We sought to evaluate cause-specific rates of encephalitis hospitalizations and predictors of inpatient mortality in the United States.
  
  
  METHODS
  Using the Nationwide Inpatient Sample (NIS) from 2000 to 2010, a retrospective observational study of 238,567 patients (mean [SD] age, 44.8 [24.0] years) hospitalized within non-federal, acute care hospitals in the U.S. with a diagnosis of encephalitis was conducted. Hospitalization rates were calculated using population-level estimates of disease from the NIS and population estimates from the United States Census Bureau. Adjusted odds of mortality were calculated for patients included in the study.
  
  
  RESULTS
  In the U.S. from 2000-2010, there were 7.3±0.2 encephalitis hospitalizations per 100,000 population (95% CI: 7.1-7.6). Encephalitis hospitalization rates were highest among females (7.6±0.2 per 100,000) and those <1 year and >65 years of age with rates of 13.5±0.9 and 14.1±0.4 per 100,000, respectively. Etiology was unknown for approximately 50% of cases. Among patients with identified etiology, viral causes were most common (48.2%), followed by Other Specified causes (32.5%), which included predominantly autoimmune conditions. The most common infectious agents were herpes simplex virus, toxoplasma, and West Nile virus. Comorbid HIV infection was present in 7.7% of hospitalizations. Average length of stay was 11.2 days with mortality of 5.6%. In regression analysis, patients with comorbid HIV/AIDS or cancer had increased odds of mortality (odds ratio [OR]  = 1.70; 95% CI: 1.30-2.22 and OR = 2.26; 95% CI: 1.88-2.71, respectively). Enteroviral, postinfectious, toxic, and Other Specified causes were associated with lower odds vs. herpes simplex encephalitis.
  
  
  CONCLUSIONS
  While encephalitis and encephalitis-related mortality impose a considerable burden in the U.S. in the 21st Century, the reported demographics of hospitalized encephalitis patients may be changing.
authors.affiliation: Center for Surgical Trials and Outcomes Research, Department of Surgery, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America; University of Rochester School of Medicine and Dentistry, Rochester, New York, United States of America.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: George
authors.affiliation: Center for Surgical Trials and Outcomes Research, Department of Surgery, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Eric B
authors.initials: EB
authors.lastname: Schneider
authors.affiliation: Johns Hopkins Encephalitis Center, Department of Neurology, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Arun
authors.initials: A
authors.lastname: Venkatesan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D016208:Databases, Factual; D004660:Encephalitis / Q000175:diagnosis / Q000453:epidemiology* / Q000266:history; D005260:Female; D049674:History, 21st Century; D017052:Hospital Mortality; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007297:Inpatients; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D014481:United States / Q000453:epidemiology; D055815:Young Adult