[1]The department of Pain;
Qinghai Province People''s Hospital;
Qinghai Xining;
810007;
[2]Ningxia International Travel Health care Center;
Yinchuan;
Ningxia750001;
China;
[3]Department of Epidemiology and Statistic at School of Public Health and Management;
Ningxia Medical University;
Yinchuan;
750004;
Elderly; Hui ethnicities; Hepatitis B surface antigen; Prevalence;