1. Division of Pulmonology, Department of Internal Medicine, Yeouido St Mary's Hospital, Seoul, Korea
2. Department of Occupational & Environmental Medicine, Seoul St Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea
3. Division of Allergy and Pulmonology, Department of Internal Medicine, Bucheon St Mary's Hospital, College of Medicine, The Catholic University of Korea, Bucheon, Korea