1. Jingyuan County Center for Disease Control and Prevention, Jingyuan 730699, China
2. Gansu Provincial Center for Disease Control and Prevention, Key Laboratory of Pathogenic Microbiology and Immunology (Gansu Province), Lanzhou 730050, China
3. Department of Health Inspection, Vaccine Research and Evaluation Center, School of Public Health, Peking University, Beijing 101100, China
4. Scientific Research Training Department, Baiyin City Center for Disease Control and Prevention, Baiyin 730900, China