1Department of Occupational and Environmental Medicine, College of Medicine, Hanyang University, Korea. ptdoctor@hanmail.net
2Department of Preventive Medicine and Institute of Occupational Medicine, Wonju College of Medicine, Yonsei University, Korea.
3Department of Preventive Medicine, College of Medicine, Seoul National University, Korea.
4Department of Preventive and Occupational Medicine, College of Medicine, Pusan National University, Korea.
5Department of Preventive Medicine, College of Medicine, Kangwon National University, Korea. JFIF d d Ducky d qhttp://ns.adobe.com/xap/1.0/