Determine the incidence and prevalence of autoimmune encephalitis (AE) among patients seen at two major health systems serving approximately 70% of residents in the state of Utah. 

The detection of AE may be increasing over time, owing to increased awareness of the diagnosis and an increasing number of validated antibody biomarkers available to aid in diagnosis. 

Adult and pediatric cases of AE diagnosed from January 1, 2014 to December 31, 2024 at two major health systems in Utah were identified through International Classification of Diseases (ICD) codes related to encephalitis and confirmed by study personnel via manual chart review in accordance with the 2016 consensus diagnostic criteria for AE. Incidence and point prevalence rates were calculated for AE and compared to those for infectious encephalitis. Geographic and demographic data were collected for AE cases. 

Patients seen in the inpatient or outpatient setting with at least 3 clinical encounters with an encephalitis ICD code were included. Manual chart review to confirm cases of AE was undertaken. We report incidence rates of AE as the number of newly confirmed cases per 100,000 person-years and point prevalence as the number of people living with AE per 100,000 persons as of January 1, 2024. Potential disparities in AE incidence and prevalence were evaluated by stratifying incidence and prevalence estimates according to geographic location, age, sex, race, and ethnicity.

Understanding the epidemiology of AE in a multi-health system population is essential for estimating healthcare demand, identifying disparities in access to care, and guiding policy decisions. This study addresses these gaps by providing accurate and contemporary incidence and prevalence data.