1. Nursing School, Peking Union Medical College, Beijing, P.R.China.
2. Division of Policy and Information, National Center for AIDS and STD Control and Prevention, China Centers for Disease Control and Prevention, Beijing, P.R.China.
3. Shijingshan District Center for Disease Control and Prevention, Beijing, P.R.China.
4. Division of Health Education and Behavioral Intervention, National Center for AIDS/STD Control and Prevention, China Center for Disease Control and Prevention, Beijing, P.R.China.
5. Department of Epidemiology, Peking Union Medical College, Beijing, P.R.China.