1. Shandong Academy of Occupational Health and Occupational Medicine, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong 250062, P.R. China
2. Department of Neurology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong 250021, P.R. China
3. Primary Health Department, Linqing Health Bureau, Linqing, Shandong 252600, P.R. China
4. Centre for Clinical Research, The University of Queensland, Brisbane, Queensland 4072, Australia