1. Shandong Center for Disease Control and Prevention, Jinan, Shandong Province, P.R. China.
2. Department of Epidemiology and Biostatistics, School of Public Health, Shandong University, Jinan, Shandong Province, P.R. China.
3. National AIDS/STD Control and Prevention, China Center for Disease Control and Prevention, Beijing, P.R. China.
4. Department of Biostatistics, Vanderbilt University, Nashville, Tennessee.
5. Department of Preventive Medicine, Vanderbilt University, Nashville, Tennessee.
6. Department of Institute for Global Health, Vanderbilt University, Nashville, Tennessee.