1. Department of Epidemiology and Statistics, West China School of Public Health, Sichuan University, Chengdu 610041, Sichuan Province, China
2. Center of Infectious Disease, West China Hospital, Sichuan University, Chengdu 610041, Sichuan Province, China
3. Center for Disease Control and Prevention of Mianyang, Mianyang 621000, Sichuan Province, China