1. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chungbuk National University Hospital, Chungbuk National University College of Medicine, Cheongju, Korea.
2. Department of Epidemiology and Health Informatics, Korea University, Seoul, Korea.
3. Department of Conservative Dentistry, Chungbuk National University Hospital, Cheongju, Korea.
4. Department of Internal Medicine, Chungbuk National University Hospital, Cheongju, Korea.
5. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea.
6. Department of Biochemistry, Chungbuk National University College of Medicine, Cheongju, Korea.
7. Division of Pulmonary Medicine and Allergy, Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Korea.