1. Medicine College of Yan'an University; Yan'an Shaanxi P. R. China
2. Department of Urology; Yangling Demonstration Zone Hospital; Yangling Shaanxi P. R. China
3. School of Public Health; Brown University; Providence Rhode Island
4. School of Public Health; Lanzhou University; Lanzhou Gansu P. R. China
5. Immunization Department of Center for Disease Control and Prevention of Xianyang; Xianyang Shaanxi P. R. China
6. School of Public Health; Shaanxi University of Chinese Medicine; Xianyang Shaanxi P. R. China