The prevalence of autoimmune hepatitis is rising: Estimates and trends from a large, multi-ethnic cohort in the United States.

BACKGROUND: Large epidemiologic studies of autoimmune hepatitis (AIH) in the United States are limited. None have reported prevalence trends over time. This contemporary study examines AIH prevalence and demographic trends over 10 years in a community-based integrated healthcare system in Northern California. We further assessed whether prevalence trends differed by AIH ascertainment approach. METHODS: This retrospective study used data from adults aged ≥18 years in Kaiser Permanente Northern California (2010-2019). AIH was identified by coded diagnosis and confirmed with diagnostic testing (laboratory and/or liver biopsy) and treatment response. Annual AIH prevalence was estimated and stratified by age, sex, and race/ethnicity. RESULTS: Among 1129 patients with confirmed AIH, 80% were female, 44% non-Hispanic White, 26% Hispanic, 16% Asian/Pacific Islander, and 9% Black. In all, 76% of patients on AIH treatment demonstrated treatment response at 6 months. AIH prevalence (per 100,000 adults) increased from 9.1 in 2010 to 18.8 in 2019 (p<0.0001). Prevalence among older adults (≥75 years) quadrupled from 10.1 to 43.7 per 100,000. Prevalence rose among all ethnicities and in 2019 was highest for Black (28.9) and Hispanic populations (25.2) per 100,000. CONCLUSIONS: AIH prevalence doubled over 10 years in a large healthcare system, with pronounced increases among older populations. Prevalence was highest among Black and Hispanic adults. Further studies should examine demographic differences in the clinical course of AIH, including response to therapy, adverse events, and outcomes.