1 Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, China; General Practice Center, Nanhai Hospital, Southern Medical University, Foshan, 528200, China; WHO Collaborating Centre for Surveillance, Research and Training of Emerging Infectious Diseases, Guangzhou, China. Electronic address: sunjiuf@163.com.
2 Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, 511430, China; WHO Collaborating Centre for Surveillance, Research and Training of Emerging Infectious Diseases, Guangzhou, China. Electronic address: wu_de68@cdcp.org.cn.