1. Department of Environmental and Occupational Health, West China School of Public Health, Sichuan University, Sichuan, China;
2. Department of Infectious Disease Prevention and Control, Hunan Provincial Center for Disease Control and Prevention, Hunan, China;
3. Department of Microbiology Laboratory, Chengdu Municipal Center for Disease Control and Prevention, Sichuan, China;
4. Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom;
5. Department of Epidemiology and Biostatistics, West China School of Public Health, Sichuan University, Sichuan, China