1. Department of Pulmonary and Critical Care Medicine, Kyung Hee University Hospital at Gang-Dong, School of Medicine, Kyung Hee University, Seoul, Korea.
2. Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
3. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
4. Department of Internal Medicine, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea.
5. Division of Pulmonology, Department of Internal Medicine, Hallym University Gangdong Sacred Heart Hospital, Seoul, Korea.
6. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
7. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
8. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Bundang CHA Medical Center, CHA University College of Medicine, Seongnam, Korea.
9. Division of Pulmonology, Department of Internal Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Guri, Korea.