1. Department of Occupational and Environmental Medicine, Ajou University Hospital, Suwon, Korea.
2. Industrial Health and Work Environment Research Institute, Korean Industrial Health Association, Seoul, Korea.
3. Department of Preventive Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea.
4. Korea Occupational Safety and Health Agency, Ulsan, Korea.
5. Department of Occupational and Environmental Medicine, Wonju Severance Christian Hospital, Wonju, Korea.