1. Department of Pulmonary, Allergy and Critical Care Medicine, Hallym University College of Medicine, Chuncheon, Korea.
2. Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea.
3. Department of Pulmonary and Critical Care Medicine, Ajou University School of Medicine, Suwon, Korea.
4. Department of Internal Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea.
5. Department of Internal Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
6. Department of Internal Medicine, Chonnam National University Medical School, Gwangju, Korea.
7. Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea.
8. Department of Internal Medicine, Chonbuk National University Medical School, Jeonju, Korea.
9. Department of Internal Medicine, Soonchunhyang University College of Medicine, Cheonan, Korea.
10. Department of Internal Medicine, Pusan National University School of Medicine, Busan, Korea.
11. Division of Respiratory and Critical Care Medicine, Department of Internal Medicine, Korea University Anam Hospital, Korea University College of Medicine, Seoul, Korea.
12. Department of Internal Medicine, Chung-Ang University College of Medicine, Seoul, Korea.
13. Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
14. Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
15. Department of Internal Medicine, The Catholic University of Korea College of Medicine, Seoul, Korea.
16. Department of Internal Medicine, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
17. Korea Centers for Disease Control & Prevention, Division of Health and Nutrition Survey, Cheongwon, Korea.