1. Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Oxford, England
2. Department of Epidemiology, School of Public Health, Peking University Health Science Centre, Beijing, China
3. China National Centre for Food Safety Risk Assessment, Chaoyang District, Beijing, China
4. Liuzhou Centre for Disease Control, Liuzhou, China
5. Liuyang Centre for Disease Control, Baiyikengdao, Liuyang, China
6. Huixian Centre for Disease Control, Huixian, China
7. Qingdao Centre for Disease Control, Qingdao, China
8. Suzhou Centre for Disease Control, Jiangsu, China
9. Department of Epidemiology, School of Public Health, Peking University Health Science Centre, Beijing, China9Head Office, Chinese Academy of Medical Science, Beijing, China