This term does not characterize a disease but a group of diseases. Annotations can be found at a more specific level (Primary hypereosinophilic syndrome, econdary hypereosinophilic syndrome, Lymphoid hypereosinophilic syndrome, Idiopathic hypereosinophilic syndrome). The prevalence is unknown varying between 0.36 and 6.3 per 100 000 (PMID:20639012)