1. State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, P. R. China
2. Department of Medical Research, Key Laboratory of Environmental Sense Organ Stress and Health of the Ministry of Environmental Protection, PLA Strategic Support Force Medical Center, Beijing, P. R. China
3. Jinan Center for Disease Control and Prevention, Jinan, P. R. China
4. Division of Infectious Disease, Key Laboratory of Surveillance and Early-Warning on Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing, P. R. China
5. Department of Statistics, Franklin College of Arts and Science, University of Georgia, Athens, Georgia, USA