1. Division of Respiratory and Critical Care, Department of Internal Medicine, Seoul Metropolitan Government-Seoul National University Boramae Medical Center, Seoul National University College of Medicine, Seoul, Korea.
2. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Hallym University Sacred Heart Hospital, Anyang, Korea.
3. Department of Internal Medicine, School of Medicine, Kyungpook National University, Daegu, Korea.
4. Department of Internal Medicine, Yeungnam University Medical Center, College of Medicine, Yeungnam University, Daegu, Korea.
5. Department of Internal Medicine, Yongin Severance Hospital, Yonsei University College of Medicine, Yongin, Korea.
6. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Keimyung University Dongsan Hospital, Daegu, Korea.
7. Division of Pulmonary, Allergy and Critical Care Medicine, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.
8. Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea.