1. Department of Occupational and Environmental Medicine, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
2. The Institute for Occupational Health, Yonsei University College of Medicine, Seoul, Korea.
3. Graduate School, Yonsei University College of Medicine, Seoul, Korea.
4. Department of Public Health, Yonsei University College of Medicine, Seoul, Korea.
5. Department of Preventive Medicine, Yonsei University College of Medicine, Seoul, Korea.