1 Department of Environmental Medicine, Ewha Womans University College of Medicine, Seoul, Korea.
2 Department of Occupational and Environmental Medicine, Hanyang University College of Medicine, Seoul, Korea.
3 Department of Occupational and Environmental Medicine, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
4 Department of Occupational and Environmental Medicine, Kosin University College of Medicine, Busan, Korea.
5 Occupational Safety and Health Research Institute, Occupational Safety and Health Agency, Ulsan, Korea.