This study compared two sampling methods - Respondent Driven Sampling (RDS) and venue-based sampling (PLACE) - to estimate the prevalence of syphilis infection among female sex workers in Liuzhou, China. RDS identified 530 sex workers and found an 8.5% syphilis prevalence, while PLACE identified 161 sex workers across 64 venues and found a higher 24% prevalence. Younger sex workers showed an even greater difference in estimated prevalence between the methods. Both methods faced challenges, and direct comparison of a single study cannot determine the true prevalence, but it provides insights into method strengths and weaknesses to improve sampling approaches.

1. Respondent Driven Sampling and Venue-Based
Sampling of Female Sex Workers Identified
Different Populations in Liuzhou, China
S. Weir1, M.G. Merli2, J. Li3, A. Gandhi4, W. Neely5, J. Edwards6, C. Suchindran7, G. Henderson8, X.-S. Chen3
1Universityof North Carolina, Epidemiology, Chapel Hill, United States, 2Duke University, Durham, United States, 3National Center for STD Control, Nanjing, China, 4Gillings School of Global Public Health,
University of North Carolina, Epidemiology, Chapel Hill, United States, 5Independent Consultant, Lake Forest Park, United States, 6Gillings School of Global Public Health, University of North Carolina, Chapel
Hill, United States, 7Gillings School of Global Public Health, University of North Carolina, Biostatistics, Chapel Hill, United States, 8School of Medicine, University of North Carolina, Chapel Hill, United States
PLACE Protocol RDS Protocol
Study Aim 培训 Interviewers and Co-PI Merli
Selection of Seeds Community Informant Interviews
• To compare two methods for sampling female sex
workers in surveys to estimate the prevalence of infection To initiate recruitment in diverse To identify a sampling frame of venues where people
strata of sex workers meet new sexual partners
in the population and describe the socio‐demographic
and behavioral characteristics of the population
• PLACE is a venue‐based method. Peer Recruitment Venue Mapping and Characterization
• Respondent Driven Sampling (RDS) is a network‐based To develop recruitment chains To determine number of sex workers (if any) at each
method. of sex workers venue in sampling frame
Interviews & Testing of
Interviews & Testing of Recruits
Workers & Patrons
To identify a sample of sex workers and estimate To identify a sample of sex workers and
% rapid test + estimate % rapid test +
Study
Location PLACE Results RDS Results
Liuzhou (population 3.6
million) in Guangxi, China Community Informant Interviews Selection of Seeds
Guangxi, on the border with 408 Community Informants identified 971 Venues 6 of 7 seeds recruited 576 sex workers to RDS office in
Vietnam, is among the provinces in in 4 urban & 6 rural districts hospital located in central urban Liuzhou.
China with the highest HIV and STI
prevalence
Venue Mapping and Interviews & Testing of Recruits in
Characterization RDS Office
Of 385 venues sampled, 334 mapped. 18 refused, 51 47 sex workers refused testing so sample is 530 sex
closed/not found/duplicate. Patrons can be excluded. workers.
Interviews of Workers
Primary Outcome Measure: Prevalence
64 venues selected. 680 Workers interviewed &
of a positive rapid test for syphilis tested at 45 of 64 venues. 161 reported sex work.
Rationale Common Definition of Sex Worker
• Biomarker outcomes not subject to self‐presentation bias PLACE
• China has a growing syphilis epidemic • 64 Venues Selected. 45 participated. (19 closed, refused)
• Rapid syphilis tests available • Sex worker sample not attained: 161 instead of 400
• No refusals among workers. Some workers missed, left early
• Weights based on probability of selection, taking into account the probability that the
venue was selected, venue refusal, and difference between workers counted vs.
interviewed
Common Elements: Both Protocols RDS
• Same geographic area • Sex Worker sample attained: 530 sex workers
• Same time period: Nov 09‐Mar 10 • 29% of those asked to participate refused invitation
• 47 refused testing, mostly reporting they had already been tested
• Same biomarker, core questions
• Same interview mode(face‐to‐face) RESULTS: Where Sex Workers Live: RESULTS: Percent of Sex Workers and
• Same applicant pool for interviewers and Percent In District of RDS Office, Other Urban PLACE Venue Workers with a Positive
District, or Rural Liuzhou County Rapid Test for Syphilis By Age
same PI
Sex Workers RDS Sex Workers -PLACE Sex Workers RDS Sex Workers -PLACE
• IRB ethical review Prevalence Ratio: 3.3
50.6 49.7 95% CI (1.5, 7.2)
• Similar payment of 100 yuan, though RDS 46.9 24 23.9 24.1
participants could get 50 more per recruit 41.2
12.6
8.5
9
Common Definition of Sex Worker 2.5
2.5
• A self‐identified female
District of RDS Other Urban Rural County All Age 15-24 Age 25+
• Aged 15 or older District
• Residing in urban or rural Liuzhou
• Who reported exchanging sex for money in the previous four weeks Lessons from the Study
• In this study, there was a significant difference in the estimated percentage of sex
workers with a positive rapid test for syphilis. The RDS estimate was 8.5%. The
PLACE estimate was 24.0%. The difference was greater among younger women
• PLACE method challenges include bias due to venue closings and venue refusals.
• RDS method challenges include bias due to differential participation based on
distance to RDS office
• One‐time comparisons can reveal method strengths and weaknesses that should
lead to method improvements. Impossible to know the truth based on one study
• The best protocols reflect engagement with community over time and local
modification based on evidence