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Eosinophils predict favorable outcomes in asthma patients with COVID-19 illness

Published online: March 1, 2021

Several studies have shown that asthma patients do not have an increased risk of severe COVID-19 disease compared with the general population. This association is not completely understood, since viral infections are known to trigger asthma exacerbations and increase asthma morbidity and mortality. The majority of asthmatics have allergic or eosinophilic asthma, characterized by elevated levels of eosinophils (eosinophilia), a type of white blood cells that is increased in allergic disorders. On the other hand, a large proportion of COVID-19 patients with moderate to severe disease have absent eosinophils in their blood. Therefore, it is thought that eosinophils may play an important, yet unknown, role in COVID-19 infections. If the type of asthma, allergic versus non-allergic, influences COVID-19 outcomes, this may have important clinical and therapeutic implications.

In a recent study published in The Journal of Allergy and Clinical Immunology: In Practice, Ferastraoaru et al sought to identify the factors predisposing to inpatient admission and subsequent mortality in a population of ethnically-diverse adult patients with asthma and COVID-19 infection. They conducted a retrospective study on 737 patients with asthma and positive COVID-19 polymerase chain reaction (PCR) tests who presented to the emergency department of a medical facility in Bronx, NY, for symptomatic COVID-19 infections between March 14 and April 27, 2020.

Ferastraoaru et al found that asthma patients with preexisting eosinophilia were significantly less likely to require hospital admission for COVID-19 compared with asthma patients with no prior eosinophilia. Overall, 85% of asthma patients admitted to the hospital had no detectable eosinophils in their blood. However, once hospitalized, those asthma patients whose eosinophil count rose above 150 cells/microliter during the hospitalization were significantly less likely to die compared with admitted asthma patients whose eosinophil counts remained below 150 cells/microliter during the admission. Moreover, preadmission eosinophil count influenced the eosinophil count trend during hospitalization. For example, those asthma patients who had eosinophilia prior to COVID-19 infection were more likely to recover their eosinophil counts during the admission for COVID-19 infection, and they eventually had better outcomes. Having eosinophilic asthma might be an important predictor for reduced COVID-19 morbidity and mortality.  Further studies are needed to explore the exact role of eosinophils in COVID-19 mortality in patients with and without asthma.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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