1. Department II of Occupational Disease, Branch of Tai'an City Central Hospital, Tai'an, Shandong 271000, P.R. China
2. Department of Public Health, Branch of Tai'an City Central Hospital, Tai'an, Shandong 271000, P.R. China
3. Occupational Disease Diagnosis, Branch of Tai'an City Central Hospital, Tai'an, Shandong 271000, P.R. China