Abstract
Background
Female sex workers (FSWs) have become one of the key populations for HIV/STI control in China. Categorization of FSWs can help prioritize HIV/STI intervention efforts. We examined two possible categorizations of FSWs and the relationship with syphilis infection risk in Liuzhou City, China.
Methods
From October 2009 to February 2010, a total of 583 FSWs recruited by respondent-driven sampling in a cross-sectional survey were tested for syphilis and interviewed to collect socio-demographic and behavioural information. Respondents were categorized based on transaction price for vaginal sex and type of sex work location. The relationship between the two categorizations and syphilis infection risk was assessed using univariate and multivariate logistic regression analysis.
Results
The prevalence rates of lifetime and active syphilis infection were 8.6% and 4.1% respectively. Lifetime and active syphilis prevalence were higher among FSWs in the lowest price category (52.7% and 25.4% respectively) and those working in streets (69.7% and 39.8% respectively) or through telephone (46.3% and 17.0% respectively). Multivariate analysis showed that lifetime syphilis prevalence was significantly higher among street-(Adjusted odds ratio AOR 38.7, 95% CI 10.7-139.9) and telephone-based FSWs (AOR 10.8, 95% CI 3.3-35.1), and that active syphilis prevalence was significantly higher among street-based FSWs (AOR 15.2, 95% CI 3.7-62.1) after adjusting for demographic and behavioural factors.
Conclusions
Categorization based on sex work location was more closely related to the risk of syphilis infection than the price classification. Street- and telephone-based FSWs had significantly higher risk of syphilis infection. Focused interventions among these particular high-risk FSWs subgroups are warranted.
Keywords: female sex workers, syphilis, respondent-driven sampling, China
Introduction
China is experiencing rising HIV and syphilis epidemics and heterosexual transmission has surpassed injection drug use transmission to become the primary mode of infection for HIV.1 Female sex workers (FSWs) are believed to play a critical role in the heterosexual transmission of HIV/STI in China. Studies have found high prevalence of syphilis infection among FSWs.2-4 Considering the role of sex work in driving and sustaining the HIV/STI epidemic particularly in countries with concentrated epidemics, it is increasingly important to understand the context and organization of female sex work to better inform HIV/STI intervention programs.5
Sex work typology which classifies FSWs into types or categories plays an important role in HIV/STI research and programming in China. The National AIDS Sentinel Surveillance Guideline in China requires that all types of entertainment establishments be systematically mapped, classified into high-, middle- and low-tiers based on high risk behaviours, and sampled proportionately within each tier.8 Many community-based surveys conducted among FSWs also take into account of sex work typology as part of their sampling strategy.9-10 From a programmatic perspective, FSWs typology can help prioritize targeted intervention efforts among high-risk FSWs subgroups.
However, the national guideline is not explicit about which indicator of risk behaviour and which criterion should be used for classifying FSWs.8 Previous studies in China have used different criteria to categorize FSWs including type of sex work location,2-3, 10-11 price charged per sexual transaction,12-13 HIV prevalence,14 and combinations of factors including work organization, relationship with managers, demographic characteristics, and income level.6 The last two criteria are not directly measurable and thus not easy to operationalize from a programmatic perspective. Some qualitative studies 12-13 applied classifications based on transactional price and observed some differences in demographic characteristics and condom use among FSW subgroups. Sex work location is directly observable and more frequently used by researchers in China and elsewhere for categorization.5, 15 But there has not been a recommended framework for conducting the classification and evaluating the linkage to actual risk of HIV/STI infection in China.
This study aimed to examine whether classification of FSWs based on price charged per sexual transaction and type of sex work location are appropriate criteria for distinguishing FSWs into subgroups at different risk of syphilis infection.
Methods
Participant recruitment
From October 2009 to January 2010, we conducted a cross-sectional study that concurrently sampled FSWs using a venue-based sampling method called “PLACE”16 and respondent-driven sampling (RDS) to compare these two methods (unpublished data) in Liuzhou City, Guangxi Zhuang Autonomous Region in southwest China. Liuzhou has a population of 3.6 million, among which 56% are non-Han ethnic minorities and Zhuang is the largest. This paper utilizes data collected through the RDS arm of that study. A participant was eligible if she (1) was at least 15 years old, (2) self-identified as female, (3) reported having exchanged sex for money in the past four weeks, (4) and was currently working and living in Liuzhou. Sex was defined to include penetrative vaginal and/or anal sex as well as oral sex.
Most RDS studies utilize a diversified initial group of participants (“seeds”) and a number of waves of recruitment to facilitate cross recruitment among subgroups and attain a sufficient sample.17 A total of 7 seeds stratified by location where clients were solicited (massage parlours, hair salons, KTVs, saunas, and parks) were recruited with help from experienced local outreach workers in our study. Each respondent was given two coded coupons and instructed to recruit peers from their social networks. Of all the coupons distributed, 54% (607/1126) were returned resulting in 583 eligible participants. The sample size was calculated using an expected 15% positive rate of rapid syphilis test (based on expert consultation) and a design effect of 3 as recommended for RDS.18 The questionnaire used to measure socio-demographic and behavioural characteristics was validated in an RDS study among FSWs in Shanghai (unpublished data) and a small pilot survey among 10 FSWs in Liuzhou. A dual incentive was offered for all participants: 100 RMB (about US$16) for completing the interview and 50 RMB (about US$8) for each successful referral. All interviews were anonymously conducted by interviewers after obtaining verbal consent in a private room. Ethical approval was obtained from Institutional Review Boards at the University of North Carolina at Chapel Hill, Duke University and the National Center for STD Control in Nanjing, China.
Syphilis testing
Presence of treponemal-specific antibodies was assessed using finger-prick rapid point-of-care (POC) syphilis test (Wantai anti-TP Antibody Rapid Test, Wantai Biological Pharmaceutical Co., Ltd, Beijing, China). Those who were positive were further tested by a toluidine red unheated serum test (TRUST, Rongsheng Biotechnical Company, Shanghai, China) to determine positivity and titres of non-treponemal-specific antibodies. Lifetime syphilis infection was defined as having a positive POC test result since treponemal-specific antibodies usually persist for life despite treatment.19-20 Active syphilis was defined as POC test positive and TRUST titre≥1:8.21-23 Forty-seven participants chose not to take the rapid POC test, mainly because they had taken the test before (36/47) or had prior syphilis infection (11/47). These participants were not significantly different from other respondents in terms of age, marital status, education level, ethnicity, and type of sex work location. All the tests were performed by trained doctors and laboratory technicians at Erkong Hospital, Liuzhou. Free treatment for syphilis infection was provided according to the national guidelines.
Data analysis
We considered two possible categorizations of FSWs. The first categorized FSWs into low-, middle- and high-paid categories based on three pricing ranges charged per vaginal sex (“price typology”): 50 RMB (about US$8) and less, 50 to 200 RMB (about US$8-32), and 200 RMB (about US$32) and above. These groupings incorporated ranges used by prior researchers and the distribution of price for vaginal intercourse found in our sample. The other classification distinguished between five categories based on the type of the most recent physical sex work location in the past six months (“location typology”): (1) KTV-based refers to those FSWs working at Karaoke bars, night clubs and bars; (2) sauna-based refers to those FSWs working at saunas and bathhouses; (3) massage-based refers to those FSWs working at massage parlours and hair salons; (4) street-based, namely those who solicited clients in public outdoor places like parks, streets, etc; (5) telephone-based was defined as a sex work location if clients were only solicited via telephone or referral through telephone in the past six months. The first three locations were referred to as entertainment establishments in previous studies on FSWs in China.9
Six of the seven seeds successfully generated 9 to 20 waves of recruitment. The six referral chains were diverse in terms of price and sex work location, except for one chain that primarily consisted of highly-paid KTV-based FSWs (see figure 1). Equilibrium was reached between 2 and 6 waves of referral with regard to age, educational attainment, marital status, ethnicity, life-time syphilis and active syphilis infection. Adjusted population proportions and 95% confidence intervals (CIs) were produced using Respondent-Driven Sampling Analysis Tool (RDSAT)24 to account for homophily, differential network size and recruitment patterns.25-26 Overlaps in confidence intervals around each population proportion estimate were compared to examine significant differences among subgroups of FSWs and to determine where significant differences lie. Individual weights for dependent variables were determined based on the RDSAT user manual and exported from RDSAT for multivariate analysis.26-27 The factors associated with syphilis infection were assessed using univariate logistic regression models and significant factors in univariate analysis were included for further assessment using multivariate logistic regression models. All data were analyzed in STATA. 28
Figure 1. Liuzhou FSWs recruitment Chains based on 6 FSWs seeds.
Results
Among those who took the POC test (n=536), 40 were positive and among these 20 were TRUST reactive with titres all ≥1:8. The prevalence rates of lifetime and active syphilis infection were estimated to be 8.6% (95% CI 5.3-12.8) and 4.1% (95% CI 2.2-6.4) respectively. Table 1 presents data on socio-demographic and behavioural characteristics and syphilis prevalence for the “price typology” of FSWs. The high-, middle- and low-paid FSWs categories accounted for 40.2%, 43.6% and 16.2% of FSWs population respectively. Compared with middle- and high-paid FSWs, low-paid FSWs had significantly higher lifetime and active syphilis prevalence and reported significantly less consistent condom use with clients in the past week (100% condom use for all sex acts). Significantly different socio-demographic profiles were found across the three price categories. High-paid FSWs were younger, better educated and mostly single. Middle-paid FSWs were relatively older, less educated, and less often single. Low-paid FSWs were even older, least educated and more often divorced or widowed. Compared with middle- and low-paid FSWs, high-paid FSWs reported significantly fewer clients in the past week. No significant difference in ethnicity, injecting drug use, and experience of HIV prevention activities at sex work locations was found.
TABLE 1.
Socio-demographic, Risk Behaviour Characteristics and Syphilis Prevalence by Different Ranges of Price Charged per Sexual Transaction among Female Sex Workers in Liuzhou City.
| Characteristics | Transaction Price categorya | ||
|---|---|---|---|
| High (N=287) APP% (95%CI) |
Middle(N=251) APP% (95%CI) |
Low (N=45) APP% (95%CI) |
|
| Total | 40.2(32.7-48.1) | 43.6(37.0-50.8) | 16.2(9.4-23.2) |
| Age group | |||
| 15-19 | 24.1(16.5-29.8) | 5.2(2.3-8.2) | 0.2(0-0) |
| 20-29 | 66(60.5-74.4) | 49.7(41.1-57.6) | 3.3(0.4-9.3) |
| 30-39 | 9.8(5.3-14.4) | 43.4(35.4-52.8) | 26.4(15.4-39.8) |
| 40- | 0.7(0-1.3) | 1.7(0-3.6) | 70.1(55.2-81.9) |
| Education | |||
| Primary or less | 10.1(4.8-16.4) | 27.3(21.2-34.7) | 77.7(59.9-82.5) |
| Junior high | 58.2(51-66.6) | 62.3(56.5-70.6) | 20.2(15.8-37.1) |
| Senior high & above | 31.7(24-38.6) | 10.4(4.6-12.9) | 2.1(0-4.9) |
| Ethnicity | |||
| Han | 52.8(45.9-60.8) | 41.4(34.3-48.6) | 24.2(15.7-37.9) |
| Zhuang | 37.1(29.8-44.7) | 50.2(42.9-57.9) | 72.9(58.7-81.2) |
| Other | 10.1(5.7-14.6) | 8.4(4.2-12.3) | 2.9(0-7.1) |
| Marital status | |||
| Never married | 87.7(82.8-91.8) | 51.8(43.7-60) | 4.2(1.3-8.7) |
| Currently married | 2.5(1.2-4.2) | 18.8(12.8-25.4) | 22.6(6.8-33.0) |
| divorced/widowed | 9.9(5.9-14.5) | 29.4(22.3-36.7) | 73.2(62.1-89.3) |
| Duration of sex work | |||
| <=2 years | 53.9(45.1-61.9) | 44.5(36.8-51.7) | 37.2(17.7-43.7) |
| 3∼4 years | 31.9(24.5-39.4) | 29.7(23.8-35.8) | 31.6(28.0-45.1) |
| >=5 years | 14.1(10.1-19.4) | 25.8(19.7-32.8) | 31.3(20.1-47.6) |
| Number of clients in the past week | |||
| <= 5 clients | 77.8(70.3-83.6) | 60.4(53.0-67.2) | 55.2(38.8-68.4) |
| >5 clients | 22.2(16.4-29.8) | 39.6(32.8-47.0) | 44.8(31.6-61.2) |
| Consistent condom use with client in the past week | 67.3(59.4-74.3) | 73.2(65.8-80.9) | 9.4(1.2-27.8) |
| Ever injected drugs | 2.4(0.1-5.5) | 2.2(0.3-4.5) | 2.9(0-8.9) |
| HIV prevention activities at sex work location | 42.5(35.5-49.4) | 54.7(45.7-61.4) | 28.2(12-43.2) |
| Known HIV status in past 12 months | 9.1(5.7-13.9) | 22.8(16.6-28.8) | 11.8(3.5-25.6) |
| Lifetime syphilis infection | 4.9(1.3-10.6) | 3.3(1.4-5.5) | 52.7(34.0-70.1) |
| Active syphilis infection | 3.5(0.2-7.4) | 1.4(0.2-2.5) | 25.4(15.3-35.3) |
Note:
transaction price categories included high as 200 RMB (about US$32) and above, middle as 50 to 200 RMB (about US$8-32), and low as 50 RMB (about US$8) and less for vaginal sex.
APP, RDS Adjusted population proportions produced; CI, confidence intervals.
Table 2 shows socio-demographic and behavioural characteristics and syphilis prevalence for the “location typology” of FSWs. The majority of FSWs were based in massage, KTV and sauna locations (38.6%, 29.6%, and 15.2% respectively), while a small proportion of FSWs were based on street (8.9%) or telephone locations (7.6%). Compared with FSWs in other categories, street- and telephone-based FSWs had significantly higher prevalence of lifetime and active syphilis infection, and reported much less frequent condom use. Socio-demographic characteristics also differed significantly among the five location categories. KTV-based FSWs were the youngest, best educated and mostly single, while street-based FSWs were the oldest, least educated, and mostly divorced or widowed. Socio-demographic characteristics for the other three categories fell in between. Telephone-based FSWs were relatively older and more often divorced or widowed compared with sauna- and massage-based FSWs. Significantly fewer street- and telephone-based FSWs reported experience of HIV prevention activities at sex work location than FSWs in other location categories. No significant difference in ethnicity and injecting drug use was found.
TABLE 2. Socio-demographic, Risk Behaviour Characteristics and Syphilis Prevalence by Sex Work locations among Female Sex Workers in Liuzhou City.
| Characteristics | KTV-based (N=174) APP% (95%CI) |
Sauna-based (N=139) APP% (95%CI) |
Massage-based (N=212) APP% (95%CI) |
Street-based (N=27) APP% (95%CI) |
Phone-based (N=31) APP% (95%CI) |
|---|---|---|---|---|---|
| Total | 29.6(15.3-48.9) | 15.2(9.7-21.1) | 38.6(26.2-49.1) | 8.9(2.9-16.2) | 7.6(3.3-12.5) |
| Age group | |||||
| 15-19 | 33.7(23.4-42.4) | 6.6(1.8-10.9) | 6.8(3.0-10.9) | 0.1(0-0) | 0.2(0-0) |
| 20-29 | 65.7(57.0-76.0) | 74.1(65.9-84.2) | 46.5(38.9-57.0) | 4.1(0-22.0) | 7.6(0-24.1) |
| 30-39 | 0.1(0-0) | 18.4(9.5-27.0) | 43.6(32.4-52.4) | 12.5(4.9-21.2) | 60.2(48.1-77.6) |
| 40- | 0.5(0-1.8) | 0.9(0-2.8) | 3.1(0-6.8) | 83.3(62.7-91.3) | 32.0(12.5-42.6) |
| Education | |||||
| Primary or less | 1.9(0.6-4.0) | 23.8(13.0-34.3) | 30.8(24.1-37.0) | 85.1(65.2-99.4) | 37.9(16.2-55.6) |
| Junior high | 49.2(40.5-58.0) | 59.6(49.7-72.0) | 61.6(55.2-69.1) | 12.3(0.6-28.6) | 58.1(40.3-79.7) |
| Senior high & above | 48.9(39.7-57.5) | 16.6(7.3-25.7) | 7.6(3.9-11.5) | 2.5(0-7.2) | 4.0(0-9.2) |
| Ethnicity | |||||
| Han | 56(47.4-64.6) | 46.8(35.4-57.8) | 36.4(30.2-45.9) | 36.9(12.9-58.0) | 52.1(28.8-73.8) |
| Zhuang | 36.4(27.9-45.8) | 41.6(31.5-53.4) | 54.2(44.5-60.3) | 59.0(37.8-83.1) | 44.5(22.5-69.0) |
| Other | 7.6(3-13.2) | 11.6(5.8-16.9) | 9.3(5.2-14.2) | 4.2(0-11.4) | 3.4(0-10.2) |
| Marital status | |||||
| Never married | 98.7(97.3-99.9) | 77.6(68.5-86.6) | 48.7(39.9-56.6) | 3.5(0.8-8.2) | 27.9(10.7-51.7) |
| Currently married | 0.1(0-0) | 9.1(3.8-14.2) | 22.0(14.8-31.1) | 5.0(0-11.8) | 9.7(0-19.5) |
| Divorced/widowed | 1.1(0.1-2.8) | 13.3(6.3-21.5) | 29.2(22.3-36.6) | 91.5(83.7-96.7) | 62.4(40.0-81.5) |
| Duration of sex work | |||||
| <=2 years | 71.5(63.0-78.2) | 33.3(21.9-44.5) | 51.4(42.3-60.8) | 23.9(9.3-41.7) | 22.8(7.7-43.0) |
| 3∼4 years | 23.2(16.8-30.4) | 50.4(37.8-61.6) | 26.0(19.5-32.2) | 40.5(21.0-48.6) | 25.5(10.3-40.7) |
| >=5 years | 5.2(2.6-9.9) | 16.3(10.4-24.7) | 22.6(15.8-29.6) | 35.6(22.4-61.5) | 51.6(33.3-68.2) |
| Number of clients in past week | |||||
| <= 5 clients | 88.8(82.3-93.8) | 50.3(37.5-61.8) | 63.9(54.4-70.9) | 24.1(9.9-40.9) | 89.8(80.2-97.8) |
| >5 clients | 11.2(6.3-17.7) | 49.7(38.2-62.5) | 36.1(29.1-45.6) | 75.9(59.1-90.1) | 10.2(2.2-19.9) |
| Consistent condom use with clients in past week | 59.2(48.5-67.0) | 80.5(71.1-87.7) | 69.3(60.0-76.9) | 17.4(0-56.3) | 40.1(21.3-62.3) |
| Ever injected drugs | 0(0-0) | 1.3(0-3.6) | 2.6(0-6.6) | 2.7(0-10.4) | 10.2(0-23.1) |
| HIV prevention activities at sex work location | 42.9(34.9-53.2) | 52.7(41.3-65.3) | 61.3(52.4-69.1) | 18.7(6.8-33.0) | 8.7(0-20.9) |
| Known HIV status in past 12 months | 10.3(5.1-16.4) | 14.2(6.4-22.5) | 22.7(16.2-30.4) | 7.0(2.7-14.2) | 10.4(1.3-23.3) |
| Lifetime syphilis infection | 4.3(0.4-9.7) | 1.9(0-4.7) | 3.0(1.0-5.3) | 69.7(49.7-82.9) | 46.3(20.6-67.1) |
| Active syphilis infection | 3.8(0.2-9.8) | 1.0(0-3.0) | 0.7(0-0.9) | 39.8(22.1-53.0) | 17.0(2.9-30.5) |
NOTE. APP, RDS Adjusted population proportions; CI, confidence intervals.
Results of multivariate logistic regression predicting lifetime and active syphilis prevalence are shown in Table 3. Lifetime syphilis prevalence was employed as a measure of lifetime risk and active syphilis infection as a marker of recent risk behaviours. After controlling for other factors, lifetime syphilis prevalence was significantly higher among street-based FSWs (Adjusted odds ratio AOR 38.7, 95% CI 10.7-139.9), telephone-based FSWs (AOR 10.8, 95% CI 3.3-35.1), those who had not received HIV testing in the past twelve months (AOR 4.2, 95% CI 1.2-15.3) and those who reported having sex with clients who were unwilling to use condoms (AOR 4.1, 95% CI 1.1-15.0). Street-based FSWs were also at higher risk of active syphilis infection (AOR 15.2, 95% CI 3.7-62.1) compared with KTV-based FSWs. Although transaction price was associated with syphilis infection in univariate analysis, it was not significantly related to syphilis infection in multivariate analysis which is probably due to its correlation with type of sex work location (Spearman rank correlation coefficient r=0.71, p<0.001). In our sample, 55% FSWs were non-Han ethnic minorities, primarily from the Zhuang, Miao and Dong ethnic minority groups. FSWs of non-Han non-Zhuang ethnic minorities were at higher risk of active syphilis infection (AOR 12.2, 95% CI 1.2, 121.9) compared to ethnically Han FSWs.
TABLE 3.
Determinants of Syphilis Infection by Multivariate Logistic Regression Analysis among Female Sex Workers in Liuzhou City.
| Characteristicsa | Lifetime syphilisa (N=536b) AORc (95%CI) |
Active syphilisa (N=532b) AORc (95%CI) |
|---|---|---|
| Type of sex work locations | ||
| KTV-based | 1.0 (ref) | 1.0 (ref) |
| Sauna-based | 0.8 (0.1-4.7) | 0.2 (0.01-2.7) |
| Massage-based | 1.1 (0.2-5.9) | 0.3 (0.03-2.4) |
| Street-based | 38.7 (10.7-139.9) | 15.2 (3.7-62.1) |
| Telephone-based | 10.8 (3.3-35.1) | 4.0 (0.6-25.4) |
| Known HIV status in the past 12 months | ||
| Yes | 1.0(ref) | |
| No | 4.2 (1.2-15.3) | |
| Refused clients who were unwilling to Use condoms in the past month | ||
| Yes | 1.0(ref) | |
| No | 4.1 (1.1-15.0) | |
| Ethnicity | ||
| Han | 1.0 (ref) | |
| Zhuang | 2.3 (0.6-8.1) | |
| Other | 12.2 (1.2-121.9) |
Positive treponemal-specific rapid syphilis test results were defined as lifetime syphilis infection. Non-treponemal-specific test titer ≥1:8 and rapid test positive were classified as active syphilis.
Participants who refused the rapid syphilis test were not included in the regression analysis.
AOR estimate was adjusted for age group, education attainment, marital status, price charged per sexual transaction, consistent condom use with clients in past week, any HIV prevention activities at place of sex work.
Discussion
In this article, we considered two classifications of FSWs based on transaction price for vaginal sex and type of sex work location, and examined whether these classifications distinguished FSW subgroups at different risk of syphilis infection. The results suggested that classification based on type of sex work location had better performance in predicting the risk of syphilis infection than the price classification. In addition, classification based on type of sex work location is more useful from an outreach perspective because it is directly observable, easy to operationalize, and able to aid in mapping and targeting of sex workers within intervention programs.5
Our results show that FSWs are operating through various locations with heterogeneous socio-demographic background and risk behaviours. We also identified a category of FSWs that only solicited clients via telephone which has not been reported in previous research on FSWs in China. Telephone-based FSWs as well as streetwalkers tended to hold highly disadvantaged socioeconomic profiles, report longer duration of sex work and a lower rate of consistent condom use. These women were also more likely to be at significantly higher risk of syphilis infection compared with FSWs working in entertainment establishments.
These features raise particular concern for several reasons. First, disease surveillance systems and most intervention studies in China have primarily targeted establishment-based FSWs.29-30 Street and telephone-based FSWs have been largely missed by intervention efforts thus far. These women are not as easily accessible as establishment-based FSWs who can be contacted through their managers who undergo regular inspections from health departments. Additionally, over 30% of the FSWs in our sample who worked in a physical location (as compared to exclusively via phone) reported that they had solicited clients through cell phones at least once in the past six months to avoid submitting commissions to managers or pimps. The increasing use of cell phones for the purpose of sex work may result in an expanding and even harder-to-reach segment of FSWs. Intervention resources should be reallocated toward these subgroups to make greater impact on containing the growing syphilis epidemic.
Secondly, like most other migrant workers in China, FSWs often do not have health insurance.31 High health care costs may place greater restriction on the affordability of testing and treatment services among street- and telephone-based FSWs who usually charge their clients much less than establishment-based FSW.32-33 Left untested and untreated, these women may be at risk to further spread syphilis, and experience devastating health consequences such as transmission to newborns causing congenital syphilis, and increased risk of HIV acquisition.34 This situation is further complicated by the fact that symptoms of early syphilis frequently go unnoticed, especially among women.35 Furthermore, syphilis infection can be persistent without adequate treatment.36
Lastly, street-based FSWs serve a large client volume in order to earn sufficient income at their lower asking price.32-33 Simultaneously, a large population of male migrant workers have created an increasing surplus male population in urban and semi-urban areas and substantial demand for low-price FSWs.37-38 Such a combination suggests the potential for an expanding syphilis epidemic in and beyond these high risk groups.
We also found that FSWs of non-Han non-Zhuang ethnic minorities were at significantly higher risk of active syphilis infection relative to FSWs of Han ethnicity. Though exploratory analysis did not find significant difference in condom use with clients among ethnic groups, FSWs of other ethnic minorities were less educated, less likely to have tested for HIV in the past year and more likely to have ever been arrested. Further studies should include sufficient number of FSWs of ethnic minorities to understand the differential impact of these factors on syphilis infection across ethnic groups. Multivariate analysis also revealed that known HIV status and refusal to have sex with clients unwilling to use condoms were both protective factors of syphilis infection in the study population. Researchers have found that high-risk populations reduce risk behaviours after having an HIV test,39 which could help explain the lower syphilis prevalence among FSWs with known HIV status. Our results indicate that a group of FSWs could exercise certain power on condom use negotiation with clients and protect themselves from syphilis infection. Experience from such groups of FSWs might be informative for other FSWs and intervention programs.
Our study is subject to limitations. Although RDS has certain advantages over other sampling methods used to sample hidden populations, empirical research has found inconsistent evidence of its ability to produce samples that faithfully represent hidden populations when compared with more conventional sampling method (unpublished findings from our main study).40 Therefore, results presented here are of uncertain generalizability to the broader population of FSWs in Liuzhou. In addition, results should be interpreted with caution as all the information collected was based on self-report. Lastly, we used the POC test as a screening test for syphilis. Studies have found that the POC test is less sensitive when performed on whole-blood specimens in the field,41-42 which may be the reason why syphilis prevalence was relatively lower than expected and lower than that found in other studies conducted among FSWs in southwest China.2-3
In conclusion, categorization of FSWs based on type of sex work location had better performance in predicting the risk of syphilis infection than the price classification. It also had important implications for designing surveillance and intervention activities in this population from a programmatic perspective. Street and telephone-based FSWs were identified as at particularly high risk of syphilis infection. Focused interventions are warranted to specifically target these subgroups of FSWs.
Acknowledgments
The authors thank all the physicians and the outreach workers in the study area for their hard work and all the respondents for their participation in the study.
Sources of Support: Support for this research was provided by the WHO Rapid Syphilis Test Project (UNICEF/UNDP/World Bank/WHO A70577), the UNC Social Science Research on HIV/AIDS in China (NIH NICHD R24 HD056670-01), RDS and PLACE comparison study (GHS-I-00-07-00002-00)
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