Respondent-Driven Sampling of Injection Drug Users in Two U.S.–Mexico Border Cities: Recruitment Dynamics and Impact on Estimates of HIV and Syphilis Prevalence

Abstract

Respondent-driven sampling (RDS), a chain referral sampling approach, is increasingly used to recruit participants from hard-to-reach populations, such as injection drug users (IDUs). Using RDS, we recruited IDUs in Tijuana and Ciudad (Cd.) Juá rez, two Mexican cities bordering San Diego, CA and El Paso, TX, respectively, and compared recruitment dynamics, reported network size, and estimates of HIV and syphilis prevalence. Between February and April 2005, we used RDS to recruit IDUs in Tijuana (15 seeds, 207 recruits) and Cd. Juá rez (9 seeds, 197 recruits), Mexico for a cross-sectional study of behavioral and contextual factors associated with HIV, HCV and syphilis infections. All subjects provided informed consent, an anonymous interview, and a venous blood sample for serologic testing of HIV, HCV, HBV (Cd. Juá rez only) and syphilis antibody. Log-linear models were used to analyze the association between the state of the recruiter and that of the recruitee in the referral chains, and population estimates of the presence of syphilis antibody were obtained, correcting for biased sampling using RDS-based estimators. Sampling of the targeted 200 recruits per city was achieved rapidly (2 months in Tijuana, 2 weeks in Cd. Juá rez). After excluding seeds and missing data, the sample prevalence of HCV, HIV and syphilis were 96.6, 1.9 and 13.5% respectively in Tijuana, and 95.3, 4.1, and 2.7% respectively in Cd. Juá rez (where HBV prevalence was 84.7%). Syphilis cases were clustered in recruitment trees. RDS-corrected estimates of syphilis antibody prevalence ranged from 12.8 to 26.8% in Tijuana and from 2.9 to 15.6% in Ciudad Juá rez, depending on how recruitment patterns were modeled, and assumptions about how network size affected an individual_s probability of being included in the sample. RDS was an effective method to rapidly recruit IDUs in these cities. Although the frequency of HIV was low, syphilis prevalence was high, particularly in Tijuana. RDS-corrected estimates of syphilis prevalence were sensitive to model assumptions, suggesting that further validation of RDS is necessary.

What Makes a Respondent-Driven Sampling “Seed” Productive? Example of Finding At-Risk Massachusetts Men Who Have Sex with Men

“…This categorization of "generative" was also chosen using evidence from prior RDS studies which suggest that only about two thirds of recruitment quotas are generally met. 12,18 Descriptive analyses were conducted using SAS® statistical software. 36 To compare generative and non-generative seeds, chi-square global tests of independence were used to examine associations between variables.…”

“…[1][2][3] Through the use of mathematical modeling and under certain strong assumptions to compensate for potential recruitment bias, RDS has been regarded as an innovative and useful means for accessing a potentially representative sample of difficult-to-reach populations at risk for or living with HIV, including injection drug users, sex workers, and men who have sex with men (MSM), both domestically and internationally. [4][5][6][7][8][9][10][11][12][13][14][15] Prior studies utilizing RDS to sample MSM have compared RDS to snowball, targeted, and time-location sampling. 9,16 In these comparisons, RDS performed similarly on ability to recruit, demonstrating the potential to successfully reach highly marginalized populations.…”

“…8,10,11 While RDS has been shown to be efficient in recruiting participants (i.e., in both effectiveness and speed at recruiting), 9,14,16 its promise of yielding representative samples has not always been supported or achieved in research practice. 12,14,17,18 Several difficulties have been identified in implementing RDS, including the possibility that reliance on incentives could motivate individuals to participate in a study even if they do not meet eligibility criteria. For example, individuals could present themselves as men who have sex with men, when in fact they may not actually have ever had sex with another man.…”

Assessing respondent-driven sampling

“…Starting from ten initial seeds, each participant recruits between 0 and 3 other individuals. The exact recruitment distribution mimics an RDS study of drug injectors in Tijuana and Ciudad Juarez, Mexico (31), in which 1∕3 of participants recruited no one, 1∕6 recruited one other participant, 1∕6 recruited two other participants, and 1∕3 recruited three other participants, the maximum allowed. The simulated recruitment procedure continues until a sample size of 500 is reached.…”

Syringe possession arrests are associated with receptive syringe sharing in two Mexico–US border cities

“…Briefly, a diverse group of 'seeds' (heterogeneous by age, gender, drug of choice and recruitment venue) were selected and given three uniquely coded coupons to refer their peers to the study. This study used 15 seeds and 207 recruits in Tijuana (n = 222) and nine seeds and 197 recruits in Ciudad Juarez (n = 206), as described previously [23], and both seeds and recruits were considered in the analysis. Waves of recruitment continued as subjects returning with coupons were each given three coupons to recruit further members from their own social networks.…”