[1] Jiangsu Prov Ctr Dis Prevent & Control, Nanjing 210009, Jiangsu, Peoples R China
[2] Univ Calif Los Angeles, Sch Publ Hlth, Dept Epidemiol, Los Angeles, CA 90024 USA
[3] Henan Prov Ctr Dis Prevent & Control, Zhengzhou, Henan, Peoples R China
[4] Chinese Ctr Dis Control & Prevent, Natl Ctr STD Control, Nanjing, Jiangsu, Peoples R China