1. Guangzhou Center for Disease Control and Prevention, Guangzhou, Guangdong Province, China
2. Institute of Public Health, Guangzhou Medical University & Guangzhou Center for Disease Control and Prevention, Guangdong, China
3. Disease Control and Prevention Department, Guangzhou Health Committee, Guangzhou, Guangdong Province, P.R. China
4. The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, China
5. Center for Disease Control and Prevention of Panyu District of Guangzhou City, Guangzhou, Guangdong Province, China
6. Guangzhou Medical University, Guangzhou, Guangdong Province, P.R. China