Encephalitis hospitalization rates and inpatient mortality in the United States, 2000-2010

PLoS One. 2014 Sep 5;9(9):e104169. doi: 10.1371/journal.pone.0104169. eCollection 2014.


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.

Publication types

  • Historical Article

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Child
  • Child, Preschool
  • Comorbidity
  • Databases, Factual
  • Encephalitis / diagnosis
  • Encephalitis / epidemiology*
  • Encephalitis / history
  • Female
  • History, 21st Century
  • Hospital Mortality*
  • Hospitalization*
  • Humans
  • Infant
  • Infant, Newborn
  • Inpatients*
  • Male
  • Middle Aged
  • Odds Ratio
  • Retrospective Studies
  • Risk Factors
  • Seasons
  • United States / epidemiology
  • Young Adult

Grant support

These authors have no support or funding to report.