Study sites and survey design
The study was conducted in eight cities in the eastern part (Changzhou and Yangzhou in Jiangsu Province) and southern part (Hezhou and Wuzhou in Guangxi Province, Jiangmen and Maoming in Guangdong Province, and Sanya and Qionghai in Hainan Province) of China. We selected cities to encompass areas where STIs are highly prevalent and where sexual contact is the main route transmission of HIV in China.
The Mega Projects were the China Ministry of Science and Technology (MOST) and Ministry of Health (MOH) projects awarded to pursue the most important public health issues in China. The current study was a baseline survey (a cross-sectional study) for one of the Mega Projects to create cohorts for analyzing the impact of expanded STI care on new HIV infection rate among high-risk groups. FSW settings were mapped and categorized in each study site and a convenience sample design was used to recruit a sample of the FSWs. Each participant was interviewed using a structured questionnaire to collect data on socio-demographic and behavioral information, and then underwent a biologic specimen collection.
Participants
Between June and September 2009, venues where FSWs solicited clients were mapped and categorized in each study site, and potential participants were identified at the different categories of venues. FSWs were recruited by outreach workers and eligibility requirements included age > 16 years (to encompass FSWs representative of those at risk for STIs); ability to give consent; and having provided commercial sex in sex-work venues or rented apartments for money or goods within the previous three months. FSWs were classified into three subgroups based on the different categories of venues where FSWs solicited clients, i.e. high-tier FSWs (HT-FSWs), middle-tier FSWs (MT-FSWs) and low-tier FSWs (LT-FSWs). High-tier group included FSWs who solicited in karaoke bars, or hotels; middle-tier group included FSWs who solicited in hair salons or barber shops, massage parlors, foot bathing shops, roadside shops, guesthouses, or roadside restaurants; and low-tier group included FSWs who solicited on the street or public outdoor places. MT-FSWs were sampled at a higher rate compared with the HT-FSW, and all accessible and acceptable LT-FSWs were recruited to allow sufficient sample sizes for analysis.
Site staff secured verbal consent from subjects to have blood drawn for free syphilis and HIV testing and to be interviewed with an anonymous and structured questionnaire by the trained outreach workers. All participants tested for syphilis and HIV were informed of their syphilis test results by an outreach team member within a week and informed of their HIV results a few weeks later. Participants with positive tests received counseling messages and were referred to designated clinics for further evaluation and possible treatment according to the national guidelines. No unique identifiers were obtained. A small gift priced at 30 yuan (around 5 US dollars) as an incentive was given to those women who agreed to participate in the survey.
The study protocols were reviewed and approved by the Medical Ethics Committee of the Chinese Academy of Medical Sciences Institute of Dermatology and National Center for Sexually Transmitted Disease Control in Nanjing.
Laboratory methods
Sera from the participants were evaluated at the STI laboratories of local CDCs or institutes of dermatology and venereology using serologic tests for determining syphilis infection according to the national algorithms. All specimens were first screened for treponemal antibody using an enzyme-linked immunosorbent assay (ELISA). Specimens with positive ELISA underwent a qualitative non-treponemal toluidine red unheated serum test (TRUST) testing, and those specimens with reactive TRUST further underwent a quantitative/titer TRUST testing. For calculating the prevalence of syphilis, the definition of syphilis infection included that specimens must have a positive ELISA and a positive TRUST [7].
Performance of the tests was evaluated on internal quality assurance procedures through re-testing all the serologically positive specimens and 10% of the negative specimens. The tests were found to have a favorable performance in the study sites.
Statistical analysis
All data from questionnaires, and laboratory results were concurrently double-entered into a computer database using EpiData Software (version 3.0) by independent research assistants, and databases were evaluated for congruency. When database entries conflicted, the original test results and surveys for these cases were retrieved to correct entered data. Prevalence of syphilis infection, with 95% confidence intervals (CIs), was measured. We used univariate and multivariate logistic regression to evaluate factors associated with syphilis infection using backward stepwise elimination. The variables attaining p < 0.10 significance in univariate analysis were included in the multivariate regression analysis, retaining only variables achieving p < 0.05 significance in the final model. Odds ratios (ORs), with 95% CIs, for risk factors for acquiring the infection were also determined. All statistical analysis was performed using Statistical Program for Social Sciences (SPSS, version 13.0, Chicago, IL) software.