1. Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan City, Shanxi Province, China
2. Department of Microbiology Test, Taiyuan Center for Disease Control and Prevention, Taiyuan City, Shanxi Province, China
3. State Key Laboratory of Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Changping, Beijing, China