1. Department of Public Health, Yantai Infectious Disease Hospital, Yantai, Shandong 264001, P.R. China
2. Department of Ultrasonic Medicine, Yantai Infectious Disease Hospital, Yantai, Shandong 264001, P.R. China
3. Department of Infectious Diseases, Yantai Infectious Disease Hospital, Yantai, Shandong 264001, P.R. China
4. Department of General Surgery, Yantai Yeda Hospital, Yantai, Shandong 264006, P.R. China