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, China. Electronic address: mawj@gdiph.org.cn.
2 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, China.