1. Department of Occupational Health, College of Medical and Public Health Sciences, Catholic University of Daegu, Gyeongsan 38430, Korea.
2. National Institute of Agricultural Sciences, Rural Development Administration, Wanju 55365, Korea.
3. Department of Infectious Diseases and BK21 PLUS, College of Veterinary Medicine, Seoul National University, Seoul 08826, Korea.
4. Department of Preventive Medicine, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea.