1. Department of Occupational Health, Chongqing Center for Disease Control and Prevention, Chongqing, China
2. National Institute of Occupational Health and Poison Control, Chinese Center for Disease Control and Prevention, Beijing, China
3. Department of Occupational Health, Beijing Municipal Center for Disease Control and Prevention, Beijing, China
4. Department of Occupational Health, Tianjin Municipal Center for Disease Control and Prevention, Tianjin, China