Association between mental illness and COVID-19 in South Korea

In their nationwide cohort study, Seung Won Lee and colleagues suggest that patients with a severe mental illness had a slightly higher risk for severe clinical outcomes of COVID-19.1 Although the authors classified region of residence into urban and rural categories to adjust for potential confounding, the high number of COVID-19 cases in Daegu (the fourth most populous city in South Korea) indicates that bias could remain due to uncontrolled confounding as a result of regional differences.