1 Department of Epidemiology, Ministry of Education Key Laboratory of Hazard Assessment and Control in Special Operational Environment, School of Public Health, Air Force Medical University, Xi'an, China.
2 Department of Epidemiology, School of Public Health, Sun Yat-sen University, Guangzhou, China.
3 School of Mathematics and Computing Science, Guilin University of Electronic Technology, Guilin, China.
4 State Key Laboratory of Infectious Disease Prevention and Control, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China.