Hypereosinophilia (HE), defined as eosinophil count greater than 1500 cell/mm3, is a rare biological finding in Emergency Department (ED). More than 200 etiologies have been reported, including allergic reactions, drug intoxications, parasitic infections or autoimmune diseases [1]. Associated diagnosis remains little known and can even be underestimated by emergency physicians. However, with an overall incidence which still approximates 0.02–0.04 new cases per 100,000 patients per year, HE can be the consequence of an acute oncological or infectious pathology and seems to be correlate with poor outcome [2, 3]. Eosinophils participate in the host defense, immune and adaptive responses, tissue damage, and airway remodeling. Eosinophils are multifunctional cells implicated in multiple processes and interact with a variety of cell types. For example, they can interact with other leukocytes and modulate their functions. Eosinophils respond to diverse signals from T cells, although T cells can also respond to signals provided by eosinophils [4] In acute phase, eosinophil proliferation include CD4 and CD8 lymphocytes mediation with interleukin-3 (IL)-3 and IL-5 secretion which activate their maturation [5, 6]. The clinical consequences result in organ invasion, explosive inflammatory response, multi-organ failure associated with a poor prognosis [7]. Although white blood cells subsets are increasingly studied, there is little consideration on eosinophilic count in ED, on account of its highly variable clinical presentation. However, this routine assay could help the clinician to stratify at-risk patients. Accordingly, the objective of this exploratory study was to assess the evolution of an unselected patients in ED with HE and identified potential factors associated with 3-month mortality.

We conducted a retrospective single-center study from January 2013 to December 2018 in the ED of a French University Hospital. All patients over 18 years who presented with hypereosinophlia (defined as eosinophil count> 1500 cell/mm3) from the initial blood sample obtained on ED admission were analyzed (IRB 443-2021-99)[1, 8]. The identification of patients was carried out exhaustively from the biology laboratory.