TrinetX Study of Hypereosinophilic Syndrome (HES) Without an Identifiable Non-haematological Secondary Cause

Inclusion Criteria: * Diagnosis record of HES (ICD-10-CM D72.11) anytime during 01 October 2020 to 30 June 2023 * At least 12 months of patient insurance record prior to first HES record. Exclusion Criteria: * Any mutation in PDGFRA, PDGFRB or FGFR1 genes (to exclude clonal HES). * History of BCR-ABL tyrosine kinase inhibitor use: imatinib, dasatinib, nolitinib, bosutinib, ponatinib, asciminib (to exclude clonal HES) * History of myeloid leukemia, myeloproliferative disorder, myelodysplastic disorder, myelomonocytic leukemia, acute erythroid leukemia, acute megakaryoblastic leukaemia, acute panmyelosis with myelofibrosis, and other specified leukaemias (to exclude reactive HES) * History of helminthiasis or use of anthelmintic medication (to exclude reactive HES) * History of autoimmune disease (to exclude reactive HES) * History of use of specific drugs: antiepileptics, sulfonamides, allopurinol, and immune checkpoint inhibitors (to exclude reactive HES)