Incidence and prevalence of hypereosinophilic syndrome in the United States: A retrospective claims database study.

BACKGROUND: Hypereosinophilic syndrome (HES) encompasses rare disorders characterized by persistent hypereosinophilia resulting in organ damage. This study assessed demographics, incidence, and prevalence of HES in the United States following the introduction of HES-specific International Classification of Diseases 10th revision, Clinical Modification (ICD-10-CM) codes in 2020. METHODS: This retrospective analysis used data from patients with HES and ≥12 months of continuous insurance coverage between October 1, 2020, and June 30, 2024, from Optum's de-identified Clinformatics® Data Mart Database. Incidence rates were calculated from the number of new HES cases divided by total person-time at risk, and prevalence from the proportion of HES cases in the population during the study. RESULTS: Overall, 695 and 1224 patients fulfilled the incident and prevalent HES case definition, respectively. The overall HES incidence rate (95% CI) was 2.01 (1.87-2.17) per 100,000 person-years, with fluctuations between 2021 and 2024. The overall HES prevalence (95% CI) was 5.32 (5.02-5.62) per 100,000 persons, with increases between 2020 and 2024. Incidence and prevalence increased with age, with an almost even female-to-male ratio (51:49). CONCLUSIONS: HES had low incidence and prevalence, with increasing prevalence from 2020 to 2024, indicating an increased recording and growing awareness of HES with ICD-10-CM codes usage.