1. Department of Preventive Medicine and Public Health and Institute for Occupational Health, Yonsei University College of Medicine, Seoul, Korea.
2. Andong Sungso Hospital, Andong, Korea.
3. Department of Occupational and Environmental Medicine, Hallym University College of Medicine, Seoul, Korea.
4. Daejeon Sun Hospital Center, Daejeon, Korea.
5. Graduate School of Public Health, Yonsei University, Seoul, Korea.