To estimate the burden of encephalitis-associated hospitalizations in the United States for 1998–2010.

Using the Nationwide Inpatient Sample, a nationally representative database of hospitalizations, estimated numbers and rates of encephalitis-associated hospitalizations for 1998–2010 were calculated. Etiology and outcome of encephalitis-associated hospitalizations were examined, as well as accompanying diagnoses listed along with encephalitis on the discharge records. Total hospital charges (in 2010 US dollars) were assessed.

An estimated 263,352 (standard error: 3,017) encephalitis-associated hospitalizations occurred in the United States during 1998–2010, which corresponds to an average of 20,258 (standard error: 232) encephalitis-associated hospitalizations per year. A fatal outcome occurred in 5.8% (95% confidence interval [CI]: 5.6%–6.0%) of all encephalitis-associated hospitalizations and in 10.1% (95% CI: 9.2%–11.2%) and 17.1% (95% CI: 14.6%–20.0%) of encephalitis-associated hospitalizations in which a code for HIV or a tissue or organ transplant was listed, respectively. The proportion of encephalitis-associated hospitalizations in which an etiology for encephalitis was specified was 50.3% (95% CI: 49.6%–51.0%) and that for which the etiology was unspecified was 49.7% (95% CI: 49.0%–50.4%). Total charges for encephalitis-associated hospitalizations in 2010 were an estimated $2.0 billion.

Encephalitis remains a major public health concern in the United States. Among the large number of encephalitis-associated hospitalizations for which an etiology is not reported may be novel infectious and noninfectious forms of encephalitis. Associated conditions such as HIV or transplantation increase the risk of a fatal outcome from an encephalitis-associated hospitalization and should be monitored.