1 Division of Pulmonary and Critical Care Medicine, Department of Medicine, Kyung Hee University, Seoul, Korea.
2 Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
3 Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea.
4 Division of Pulmonary and Critical Care Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Guri, Korea.
5 Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Hallym University Chuncheon Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
6 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.
7 Regional Center for Respiratory Disease, Yeungnam University Medical Center, Yeungnam University College of Medicine, Daegu, Korea.
8 Division of Respiratory and Critical Care Medicine, Department of Internal Medicine, College of Medicine, Korea University, Seoul, Korea.
9 Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Yeouido St Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
10 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.