Association between eosinophil counts and outcomes of severe coronavirus disease 2019 in elderly asthma patients: a prospective cohort study.

Background: Given effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on the respiratory system and epidemiological burden of asthma worldwide, coronavirus disease 2019 (COVID-19) in asthma patients caused reasonable concern to be a "dangerous" combination in early pandemic. This is especially pertinent to elderly patients with asthma since older age, diabetes, cardiovascular disease, and hypertension, is associated with more serious complications of COVID-19 and higher mortality. Blood eosinopenia occurs as a part of the total cytopenia at the early stage of severe COVID-19 due to an effect of SARS-CoV-2 virus on the immunity and severe inflammation. Therefore, blood cell count monitoring could be useful for the diagnosis and outcome prediction in COVID-19. The aim of this study was to investigate a relationship between blood eosinophil count and outcomes of COVID-associated lung injury in elderly patients with asthma. Methods: This was a prospective cohort study involving elderly patients with asthma (>60 years of age, n=131). All patients were admitted to a hospital for COVID-19 from October 1, 2020, to September 30, 2021. Those patients who completed their hospital treatment (were discharged or died) by December, 30, 2021, were enrolled in the study. All the patients were previously diagnosed with asthma according to Global Initiative for Asthma (GINA) criteria. The diagnosis of COVID-19 was confirmed by positive polymerase chain reaction (PCR) test, typical clinical symptoms, and radiological signs of multifocal pneumonia. Survived patients were followed up by weekly phone calls for 90 days after discharge. The complete blood count was measured in the whole blood samples obtained at admission. Hazard ratio was calculated using univariable and multivariable Cox proportional hazards regression models. Results: In total, 131 patients were enrolled in the study. Eighty-six patients survived, 30 patients died in the hospital, and 15 patients died post-discharge. Common independent predictors of death were the Charlson Comorbidity Index and eosinopenia. Survived patients had higher blood eosinophil count compared to patients who died in the hospital or post-discharge (P=0.001 and P=0.04, respectively). The cut-off eosinophil count was estimated as 100 cells/L; higher eosinophil count was seen in 24% of survivors and in none of non-survivors (P=0.002 and P=0.04, respectively). The absolute eosinophil count was a significant predictor of in-hospital death [odds ratio (OR), 0.64; 95% confidence interval (CI): 0.49-0.84; P=0.002] and death post-discharge (OR, 0.78; 95% CI: 0.65-0.95; P=0.01). Median survival, in-hospital and post-discharge, was shorter in patients with eosinophil count ≤100 cells/L (P<0.001 and P=0.04, respectively). Conclusions: Blood eosinophil count could be used as a prognostic marker of outcome in elderly patients with asthma and COVID-associated lung injury. Eosinophil level ≤100 cells/µL could be used as a threshold for predicting poor outcome, both in-hospital and 90-day post-discharge.