1. Department of Occupational and Environmental Medicine, Dongguk University Gyeongju Hospital, Gyeongju, Korea.
2. Department of Preventive Medicine, Dongguk University Gyeongju Hospital, Gyeongju, Korea.
3. Department of Medicine, Graduate School of Kyungpook National University, Daegu, Korea.
4. Department of Occupational and Environmental Medicine, Yeungnam University Hospital, Daegu, Korea.