1. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Yeouido St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
2. Division of Pulmonology and Critical Care Medicine, Department of Internal Medicine, Uijeongbu St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Uijeongbu, Korea.
3. Division of Pulmonary and Allergy, Department of Internal Medicine, Regional Respiratory Center, Yeungnam University Hospital, Daegu, Korea.
4. Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
5. 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.
6. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Bucheon St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Bucheon, Korea.
7. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Ilsan Paik Hospital, Inje University College of Medicine, Goyang, Korea.
8. Division of Pulmonology, Department of Internal Medicine, St. Vincent's Hospital, College of Medicine, The Catholic University of Korea, Suwon, Korea.
9. Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Internal Medicine, Chung-Ang University College of Medicine, Seoul, Korea.
10. Division of Pulmonary and Critical Care Medicine, Chungnam University Medical Center, Daejeon, Korea.
11. Department of Internal Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Guri, Korea.
12. Department of Pulmonary and Critical Care Medicine, Kyung Hee University Hospital at Gangdong, Seoul, Korea.
13. Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Korea.
14. Division of Pulmonary, Department of Internal Medicine, Korea University Ansan Hospital, Ansan, Korea.
15. Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, St. Paul's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
16. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul Metropolitan Government-Seoul National University Boramae Medical Center, Seoul National University College of Medicine, Seoul, Korea.
17. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea.
18. Division of Pulmonary, Allergy and Critical Care Medicine, Hallym University Kangnam Sacred Heart Hospital, Seoul, Korea.
19. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Wonkwang University Sanbon Hospital, Wonkwang University School of Medicine, Gunpo, Korea.