1. Department of epidemiology and health statistics, Qingdao University medical college, Qingdao, China
2. Department of Second Supervisory Section, Shibei District Health Supervision Institute, Qingdao, China
3. Department of Occupational Health, Qingdao Municipal Centers for Disease Control and Prevention, Qingdao, China
4. Department of Planned Immunization, Shandong Center for Disease Control and Prevention, Jinan, China