BACKGROUND: The coronavirus disease-2019 (COVID-19) is still rapidly spreading worldwide, and remains a global health crisis. We investigated the impact of asthma on the prevalence and outcomes of COVID-19 and identify the risk factors for delayed viral clearance. METHODS: Adult patients with COVID-19 admitted to 10 hospitals in Daegu were retrospectively registered, and their clinical information was collected. Delayed viral clearance was divided into two groups based on 30 days. RESULTS: A total of 2,200 patents were evaluated, and the prevalence of asthma in COVID-19 was 3.2%. Compared with Korea nationwide survey data, there were no differences in asthma prevalence. In the univariate analysis, the risk of death (13.6% vs 6.4%, P = 0.021) and high flow oxygen therapy (18.2% vs 10.5%, P = 0,048) was increased in asthma patients, with a stronger tendency among elderly, women, and overweight patients. However, in a multivariate analysis using the logistic regression model, any clinical outcomes according to asthma was not significant. The risk factors for delayed viral clearance were older age >65 years (Odds ratio [95% confidence interval] 2.002 [1.292–3101]), dementia (3.123 [1.833–5.321]), skin rash (15.943 [1.613–157.535]), and anemia (2.156 [1.061–2.377]), whereas headache (0.673 [0.485–0.932]) lowered the risk. CONCLUSIONS: There may be a difference depending on phenotypes, but asthma prevalence was not significantly different in patients with COVID-19, and asthma did not affect outcomes of COVID-19. Older age, dementia, headache, skin rash, and anemia were independently associated with delayed viral clearance.