Severe eosinophilia is defined as an absolute eosinophil count (AEC) in the peripheral blood more than or equal to 5 K/μL. Hypereosinophilia (HE) is defined as AEC more than or equal to 1.5 K/μL recorded on at least 2 occasions at least 4 weeks apart.1,2 The clinical significance of severe eosinophilia and HE lies in their potential to indicate hypereosinophilic syndrome (HES) and the risk of target organ damage.1,3,4 However, data on pediatric patients are limited. Therefore, this study aims to identify potential etiologies, clinical courses, and outcomes of severe eosinophilia and HE in pediatric patients at a US tertiary care center.

Eosinophilic asthma is associated with frequent exacerbations, but the relevance of peripheral eosinophil count at the time of exacerbation is unknown.

Oral immunotherapy (OIT) is a proactive approach to modulate acute IgE-mediated hypersensitivity responses to food through incremental allergen exposure. Gastrointestinal adverse events (AEs) are common and can represent a major obstacle to successful desensitization. In a smaller proportion of patients, OIT may induce eosinophilic esophagitis (EoE), a chronic delayed hypersensitivity response associated with tissue eosinophilia and esophageal dysfunction. Notably, there have also been case reports of nonesophageal eosinophilic gastrointestinal diseases developing during OIT.