1. Department of Internal Medicine, Veterans Health Service Medical Center, Seoul, Korea.
2. Department of Allergy and Clinical Immunology, Airway Sensation and Cough Research Laboratory, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
3. Department of Internal Medicine, Kyung Hee University Medical Center, Seoul, Korea.
4. Division of Allergy and Clinical Immunology, Department of Internal Medicine, Chungbuk National University Hospital, Cheongju, Korea.
5. Department of Internal Medicine, Gachon University Gil Medical Center, Incheon, Korea.
6. Respiratory Research Group, Hull York Medical School, Castle Hill Hospital, University of Hull, Cottingham, United Kingdom.
7. Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.