1. Division of Pulmonology and Allergy, Department of Internal Medicine, Gachon University Gil Medical Center, Gachon University College of Medicine, Incheon, Korea.
2. Division of Pulmonology and Allergy, Department of Internal Medicine, Veterans Health Service Medical Center, Seoul, Korea.
3. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Chung-Ang University Gwangmyeong Hospital, Chung-Ang University College of Medicine, Seoul, Korea.