1. Department of Social and Preventive Medicine, College of Medicine, Inha University, Incheon, Korea
2. Department of Occupational and Environmental Medicine, Ewha Womans University College of Medicine, Seoul, Korea
3. Department of Occupational and Environmental Medicine, College of Medicine, Inha University, Incheon, Korea
4. Department of Pediatrics, College of Medicine, Inha University, Incheon, Korea
5. Department of Preventive Medicine, College of Medicine, Dankook University, Cheonan, Korea
6. Department of Pediatrics, Asan Medical Center, College of Medicine, University of Ulsan, Seoul, Korea