1. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center; Sungkyunkwan University School of Medicine; Seoul South Korea
2. Department of Critical Care Medicine, Samsung Medical Center; Sungkyunkwan University School of Medicine; Seoul South Korea
3. Departments of Epidemiology and Medicine, Welch Center for Prevention, Epidemiology and Clinical Research; Johns Hopkins Bloomberg School of Public Health; Baltimore Maryland USA