1. Division of Pulmonology, Department of Internal Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Korea.
2. Divisions of Preventive, Occupational & Aerospace Medicine and Pulmonary & Critical Care Medicine, Mayo Clinic, Rochester, MN, USA.
3. Department of Occupational and Environmental Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Korea.