1. Guangdong Provincial Institute of Public Health Guangdong Provincial Center for Disease Control and Prevention Guangzhou China
2. Guangdong Provincial Center for Disease Control and Prevention Guangzhou China
3. Shenzhen Center for Disease Control and Prevention Shenzhen China
4. Department of Epidemiology and Biostatistics University of Georgia Athens Georgia USA
5. State Key Laboratory of Emerging Infectious Diseases, School of Public Health The University of Hong Kong, HKSAR Hong Kong China