1 Key Laboratory of Surveillance and Early-warning on Infectious Disease, Division of Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing 102206, China.
2 Beijing Center for Disease Control and Prevention.
3 School of Public Health, Fudan University.
4 Guangzhou Center for Disease Control and Prevention.
5 Huaxin Hospital, the First Affiliated Hospital of Tsinghua University.
6 Key Laboratory of Surveillance and Early-warning on Infectious Disease,Division of Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing 102206, China. Email: yuhj@ chinacdc.cn.