1. Department of Occupational Medicine and Clinical Toxicology, Taipei Veterans General Hospital , Taipei , Taiwan
2. Office of Preventive Medicine, Centers for Disease Control, Ministry of Health and Welfare , Taipei , Taiwan
3. School of Medicine, College of Medicine, National Yang Ming Chiao Tung University , Taipei , Taiwan
4. Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University , Taipei , Taiwan
5. Institute of Environmental and Occupational Health Sciences, College of Medicine, National Yang Ming Chiao Tung University , Taipei , Taiwan