In patients with asthma, the presence of preexisting eosinophilia was protective against coronavirus disease 2019 (COVID-19)-associated hospital admission, with the development of eosinophilia during hospitalization associated with decreased rates of mortality. Researchers conducted a retrospective study  among adult patients (aged ≥18 years) who had tested positive for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection by polymerase chain reaction (PCR) at the Albert Einstein College of Medicine/Montefiore Medical Center in Bronx, New York, between March 14 and April 27, 2020. Results of the analysis were published in The Journal of Allergy and Clinical Immunology: In Practice.

Investigators sought to identify risk factors associated with hospitalization and subsequent mortality in patients with COVID-19 with asthma. Among those who were hospitalized, comorbidities, laboratory results, and mortality rates were recorded. During the study period, a total of 6445 patients tested positive via PCR for SARS-CoV-2. Among these individuals, 4558 had been seen previously in the same healthcare system at least 1 time during the last 10 years — that is, prior to their infection with COVID-19.

Overall, 20.9% (951 of 4558) of patients infected with COVID-19 had a diagnosis of asthma. Among those with asthma, 77.5% (737 of 951) had been seen in the emergency department (ED), and 78.8% (581 of 737) of those with asthma who were evaluated in the ED were admitted to the hospital. Among all patients with COVID-19 — both with and without asthma — hypertension and diabetes were the most frequently associated comorbidities (60.6% and 41.4%, respectively).

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Results of the study showed that individuals with prior eosinophilia (that is, those with previously measured mean absolute eosinophil count [AECs] of ≥150 cells/µL) were significantly less likely to be admitted to the hospital from the ED (odds ratio [OR], 0.46; 95% CI, 0.21 to 0.98; P =.04). Patients with asthma and comorbid congestive heart failure, chronic kidney disease, and chronic obstructive pulmonary disease, however, were more likely to be hospitalized.

Further, hospitalized patients with asthma and peak hospital-measured AEC of 150 cells/µL or higher (n=104) were significantly less likely to die compared with those whose AECs never increased to above 150 cells/µL (n=213; mortality rates: 9.6% vs 25.8%, respectively; OR, 0.006; 95% CI, 0.0001-0.64; P =.03). Patients with asthma whose AECs increased to 150 cells/µL or higher during hospital admission also had significantly higher mean pre-COVID-19 AECs compared with those whose AECs never increased to above 150 cells/µL (237±181 vs 163±147 cells/µL, respectively; OR, 2012; 95% CI, 27.3-14,816; P =.001).

The researchers concluded that additional prospective and mechanistic studies are warranted to explore the exact role played by eosinophils in COVID-19 mortality, along with the influence of a variety of asthma characteristics on outcomes among patients with asthma and COVID-19 infection.


Ferastraoaru D, Hudes G, Jerschow E, et al. Eosinophilia in asthma patients is protective against severe COVID-19 illness. J Allergy Clin Immunol Pract. Published online January 23, 2021. doi:10.1016/j.jaip.2020.12.045