1. Department of Occupational and Environmental Health, College of Public Health, Zhengzhou University, Zhengzhou, China
2. Department of Epidemiology and Biostatistics, College of Public Health, Zhengzhou University, Zhengzhou, China
3. Department of Occupational Health, Henan Institute of Occupational Medicine, Zhengzhou, China
4. Clinical Department, Zhengzhou Institute of Occupational Health, Zhengzhou, China