1. Division of Respiratory and Allergy, Department of Internal Medicine, Soonchunhyang University Bucheon Hospital, Soonchunhyang University College of Medicine, Bucheon, Korea.
2. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Inha University College of Medicine, Incheon, Korea.
3. Department of Internal Medicine, Gachon University Gil Medical Center, Incheon, Korea.
4. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Wonkwang University School of Medicine, Iksan, Korea.
5. Division of Allergy and Pulmonology, Department of Internal Medicine, Bucheon St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Bucheon, Korea.
6. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.