Evaluating respondent-driven sampling in a major metropolitan area: Comparing injection drug users in the 2005 Seattle area national HIV behavioral surveillance system survey with participants in the RAVEN and Kiwi studies

Assessing reliability of naïve respondent-driven sampling samples by using repeated surveys among people who inject drugs (PWID) in New Jersey

INTRODUCTION

Respondent-driven sampling (RDS) is widely used to sample populations with higher risk of HIV infection for whom no sampling frames exist. However, few studies have been done to assess the reliability of RDS in real world settings.

METHODS

We assessed the reliability of naïve RDS samples using five rounds of the National HIV Behavioral Surveillance - People Who Inject Drugs surveys in Newark, New Jersey from 2005 to 2018. Specifically, we compared the distributions of time-insensitive demographic characteristics in temporally adjacent RDS samples with Monte Carlo Two-Sample Kolmogorov-Smirnov Test with 100,000 replicates. The distributions of time-sensitive demographic characteristics were also compared as sensitivity analyses.

RESULTS

The study showed that repeated RDS samples among people who inject drugs in the greater Newark area, New Jersey were reliable in most of time-insensitive demographics and recruitment homophily statistics. Sensitivity analyses of time-sensitive demographics also presented consistencies in most of temporally adjacent samples.

CONCLUSIONS

In conclusion, RDS has the potential to provide reliable samples, but demographic characteristics of RDS samples may be easily biased by homophily. Future studies using RDS may need to pay more attention to potential homophily bias and consider necessary diagnostic procedures and sample adjustments.

Socioeconomic and racial/ethnic spatial polarization and incarceration among people who inject drugs in 19 US metropolitan areas, 2015

The purpose of this study is to test, for the first time, the association between spatial social polarization and incarceration among people who inject drugs (PWID) in 19 large U.S. metropolitan statistical areas (MSAs) in 2015. PWID were recruited from MSAs for the Centers for Disease Control and Prevention's 2015 National HIV Behavioral Surveillance. Administrative data were used to describe the ZIP-code areas, counties, and MSAs where PWID lived. We operationalized spatial polarization using the Index of Concentration at the Extremes (ICE), a measure that reflects polarization in race and household income at the ZIP-code level. We tested the association between spatial polarization and odds of past-year arrest and detainment using multilevel multivariable models. We found 37% of the sample reported being incarcerated in the past year. Report of past-year incarceration varied by race/ethnicity: 45% of non-Hispanic white PWID reported past-year incarceration, as did 25% of non-Hispanic Black PWID, and 43% of Hispanic/Latino PWID (N = 9047). Adjusted odds ratios suggest that Black PWID living in ZIP-code areas with a higher ICE score, meaning more white and affluent, had higher odds of past-year incarceration, compared to white PWID. In previous research, incarceration has been found to be associated with HIV acquisition and can deter PWID from engaging in harm reduction activities.

Methodological and Ethical Considerations in Research With Immigrant and Refugee Survivors of Intimate Partner Violence

To promote safe and positive health outcomes by utilizing culturally relevant evidence-based interventions for immigrant and refugee women survivors of intimate partner violence, their active participation in research is critical. With 43.6 million immigrants and refugees living in the United States, there is a need for research studies to eliminate health disparities in these populations. However, barriers to recruiting and retaining these populations in research prevent the provision of quality and culturally informed services to meet their needs. The aim of this article is to discuss the recruitment and retention strategies employed and analyze the methodological and ethical challenges in the context of the weWomen Study. The use of a multifaceted approach informed by best practices maximized recruitment efforts and active participation that generated high numbers of immigrant and refugee women participants. The study also substantiated the need for more community-based participatory approaches to engage community members in the development of culturally appropriate approaches that instill a sense of ownership over the research process. Active research participation of immigrant and refugee survivors will help investigators understand their unique needs and facilitate the implementation of targeted evidence-based interventions.

An application of agent-based modeling to explore the impact of decreasing incarceration rates and increasing drug treatment access on sero-discordant partnerships among people who inject drugs

BACKGROUND

People who inject drugs (PWID) lag behind other key populations in HIV care continuum outcomes. The impacts of criminal justice reform and increasing drug treatment access on HIV have been underexplored.

METHODS

We developed agent-based models (ABM) of sexual partnerships among PWID and non-PWID, and injection equipment-sharing partnerships among PWID in five US cities (Baltimore, Boston, Miami, New York City, San Francisco) over 3 years. The first set of ABM projected changes in partnership discordance among PWID as a function of decreasing ZIP code-level incarceration rates. The second set projected discordance as a function of increasing ZIP code-level drug treatment access. ABM were parameterized and validated overall, and by city and PWID race/ethnicity (Black, Latino, White) using National HIV Behavioral Surveillance data, administrative ZIP code-level data, surveillance reports and prior literature. Informed by research on prisoner release and community-level HIV prevalence, reductions in incarceration rates were fixed at 5% and 30% and respectively projected to increase ZIP code-level HIV prevalence by 2% and 12%. Increases in drug treatment access were fixed at 30% and 58%.

RESULTS

In each city, a 30% reduction in ZIP code-level incarceration rates and 12% increase in ZIP code-level HIV prevalence significantly increased sero-discordance among at least one racial/ethnic group of PWID by 1-3 percentage points. A 5% reduction in incarceration rates, and 30% and 58% increases in drug treatment access, led to isolated significant changes in sero-discordance among Black and White PWID that were less than 1 percentage point.

CONCLUSION

Reductions in incarceration rates may lead to short-term increases in sero-discordant partnerships among some PWID by increasing community-level HIV prevalence. Efforts to increase HIV testing, engagement in care and community reintegration post release, should be strengthened in the wake of incarceration reform. Additional research should confirm these findings and explore the lack of widespread impacts of drug treatment in this study.

The Impact of Syringe Services Program Policy on Risk Behaviors Among Persons Who Inject Drugs in 3 US Cities, 2005-2015

OBJECTIVES

The impact of a syringe services program (SSP) policy on risk behaviors and its durability are not as well studied as the impact of the SSPs themselves. We examined whether trends in syringe sharing among persons who inject drugs (PWID) were associated with changes to syringe access policies in 3 US cities: Denver, New Orleans, and Philadelphia.

METHODS

PWID were surveyed through National HIV Behavioral Surveillance System surveys in each city in 2005, 2009, 2012, and 2015. We assessed changes in syringe sharing from 2005 to 2015 by city. We used multivariable stepwise logistic regression analysis to measure the associations among syringe sharing and injection works sharing, time, and SSP access.

RESULTS

From 2005 to 2015, syringe sharing decreased significantly from 49.1% to 33.1% in Denver (P < .001), increased significantly from 32.0% to 50.5% in New Orleans (P < .001), and remained unchanged in Philadelphia (30.4% to 31.5%; P = .87). Compared with persons who obtained syringes from any nonsterile source, the adjusted odds of syringe sharing among PWID were significantly lower in each city if syringes were obtained from sterile sources only: Denver adjusted odds ratio (aOR) = 0.23 (95% confidence interval [CI], 0.18-0.30; New Orleans aOR = 0.26 (95% CI, 0.19-0.35), and Philadelphia aOR = 0.43 (95% CI, 0.33-0.57).

CONCLUSIONS

The lowest proportion of PWID reporting syringe sharing was in Philadelphia, which has a long-standing legal SSP. Implementation of a legal SSP in Denver in 2012 corresponded to a decrease in sharing, whereas the lack of a legal SSP in New Orleans corresponded to an increase in sharing. Universal long-term access to legal SSPs could further the progress made in HIV prevention among PWID.

Respondent Driven Sampling for Immigrant Populations: A Health Survey of Foreign-Born Korean Americans

This study examined feasibility and methodological utilities of respondent driven sampling (RDS) for Korean immigrants. We conducted the Health and Life Study of Koreans (HLSK), a Web-based RDS study targeting foreign-born Korean Americans. Through chain referrals, n = 638 participated. Geographic coverage and estimates of HLSK were compared to foreignborn Korean samples in the American Community Survey and the California Health Interview Survey as benchmarks. Compared to the benchmarks, HLSK fared well on the geographic coverage, household type and size, employment and health insurance but over-captured those who were younger, more recent immigrants, with higher education and with disability. Existing RDS-specific estimators were largely ineffective. Conclusions. RDS may serve as a cost-effective tool for recruiting recent immigrants, a harder-to-recruit subgroup within minorities. However, recruitment noncooperation posed operational challenges, a critical gap in the literature. This leaves RDS yet to be a reliable methodology.

Network-Based Research on Rural Opioid Use: an Overview of Methods and Lessons Learned

PURPOSE OF REVIEW

The purpose of this paper is to provide a thorough overview of methods used for recruitment, network data collection, and network data management in a network-based study of rural people who use drugs (PWUD) and to offer methodological recommendations for future research on rural drug use.

RECENT FINDINGS

The Social Networks among Appalachian People (SNAP) study recruited a cohort of 503 rural PWUD via respondent-driven sampling (RDS) and has retained more than 80% of eligible participants over 7-9 years. SNAP has yielded important methodological insights, including that (1) RDS referral was non-random and disproportionately involved kin and (2) interviewer-administered questionnaires were successful in eliciting accurate name and age information about network members. The SNAP experience suggests that RDS was a successful recruitment strategy for rural PWUD and questionnaires administered by community-based interviewers in the context of a Certificate of Confidentiality could elicit detailed data on PWUD risk networks.

Brief Report: Nonfatal Overdose Events Among Persons Who Inject Drugs: Findings From Seven National HIV Behavioral Surveillance Cities 2009 & 2012

The rate of drug and opioid overdose deaths in the United States has more than tripled over the past 15 years. The ability to conduct public health surveillance on nonfatal overdoses is limited. The current study used National HIV Behavioral Surveillance (NHBS) data to estimate recent and lifetime history of nonfatal overdose events in persons who inject drugs in 7 cities. Recent and lifetime experience of overdose events ranged from 3% to 20% and from 29% to 63%, respectively. Adapting systems such as NHBS may be useful in responding to and monitoring emergent public health problems such as the overdose epidemic.

A Decline in HIV Testing Among Persons Who Inject Drugs in the Seattle Area, 2004-2015

BACKGROUND

Promoting HIV testing is a key component of the public health response to HIV. Assessing HIV testing frequency among persons who inject drugs (PWID) monitors the status of these efforts and can identify unmet needs and opportunities to more effectively promote testing.

METHODS

Data were combined from 4 Seattle-area surveys of PWID from the National HIV Behavioral Surveillance (NHBS) program (2005-2015) and 6 surveys of Needle Exchange clients (2004-2015).

RESULTS

The proportion of PWID reporting an HIV test in the previous 12 months declined from 64% in 2005% to 47% in 2015 in the NHBS surveys and from 72% to 58% in the Needle Exchange surveys. These declines persisted in multivariate analyses controlling for differences in the study populations in age, race, sex, area of residence, education, current homelessness, drug most frequently injected, daily injection frequency, and combined male-to-male sex and amphetamine injection status. The proportion of NHBS participants reporting not knowing the HIV status of their last injection partner increased from 38% to 45%. The proportion not knowing the HIV status of their last sex partner increased from 27% to 38%.

CONCLUSIONS

A decrease in HIV testing was found in 2 independent Seattle-area study populations. This was complemented by increases in the proportions not knowing the HIV status of their last sex and last injection partners. Research is needed to ascertain if such declines are observed elsewhere, the reasons for the decline, and appropriate means to effectively attain optimal HIV testing frequency among PWID.

Comparison of Three Popular Methods for Recruiting Young Persons Who Inject Drugs for Interventional Studies

Persons who inject drugs (PWID) are at risk for adverse health outcomes as a result of their drug use, and the resulting social stigma makes this a difficult population to reach for interventions aimed at reducing morbidity and mortality. During our study of adult PWID aged ≤40 years living in San Diego during 2009 and 2010, we compared three different sampling methods: respondent-driven sampling (RDS), venue-based sampling at one syringe exchange program (SEP), and street-based outreach. We compared demographic, socioeconomic, health, and behavioral factors and tested participants for HIV, hepatitis B virus (HBV), and hepatitis C virus (HCV) and compared across the three methods. Overall, 561 (74.8%) of the targeted 750 PWID were enrolled. Venue-based convenience sampling enrolled 96% (242/250) of the targeted participants, followed closely by street-based outreach with 92% (232/250) recruited. While RDS yielded the fewest recruits, producing only 35% (87/250) of the expected participants, those recruited through RDS were more likely to be female, more racially diverse, and younger.

Cross-sectional association between ZIP code-level gentrification and homelessness among a large community-based sample of people who inject drugs in 19 US cities

BACKGROUND

Housing instability has been associated with poor health outcomes among people who inject drugs (PWID). This study investigates the associations of local-level housing and economic conditions with homelessness among a large sample of PWID, which is an underexplored topic to date.

METHODS

PWID in this cross-sectional study were recruited from 19 large cities in the USA as part of National HIV Behavioral Surveillance. PWID provided self-reported information on demographics, behaviours and life events. Homelessness was defined as residing on the street, in a shelter, in a single room occupancy hotel, or in a car or temporarily residing with friends or relatives any time in the past year. Data on county-level rental housing unaffordability and demand for assisted housing units, and ZIP code-level gentrification (eg, index of percent increases in non-Hispanic white residents, household income, gross rent from 1990 to 2009) and economic deprivation were collected from the US Census Bureau and Department of Housing and Urban Development. Multilevel models evaluated the associations of local economic and housing characteristics with homelessness.

RESULTS

Sixty percent (5394/8992) of the participants reported homelessness in the past year. The multivariable model demonstrated that PWID living in ZIP codes with higher levels of gentrification had higher odds of homelessness in the past year (gentrification: adjusted OR=1.11, 95% CI=1.04 to 1.17).

CONCLUSIONS

Additional research is needed to determine the mechanisms through which gentrification increases homelessness among PWID to develop appropriate community-level interventions.

Associations of place characteristics with HIV and HCV risk behaviors among racial/ethnic groups of people who inject drugs in the United States

PURPOSE

Investigate whether characteristics of geographic areas are associated with condomless sex and injection-related risk behavior among racial/ethnic groups of people who inject drugs (PWID) in the United States.

METHODS

PWID were recruited from 19 metropolitan statistical areas for 2009 National HIV Behavioral Surveillance. Administrative data described ZIP codes, counties, and metropolitan statistical areas where PWID lived. Multilevel models, stratified by racial/ethnic groups, were used to assess relationships of place-based characteristics to condomless sex and injection-related risk behavior (sharing injection equipment).

RESULTS

Among black PWID, living in the South (vs. Northeast) was associated with injection-related risk behavior (adjusted odds ratio [AOR] = 2.24, 95% confidence interval [CI] = 1.21-4.17; P = .011), and living in counties with higher percentages of unaffordable rental housing was associated with condomless sex (AOR = 1.02, 95% CI = 1.00-1.04; P = .046). Among white PWID, living in ZIP codes with greater access to drug treatment was negatively associated with condomless sex (AOR = 0.93, 95% CI = 0.88-1.00; P = .038).

CONCLUSIONS

Policies that increase access to affordable housing and drug treatment may make environments more conducive to safe sexual behaviors among black and white PWID. Future research designed to longitudinally explore the association between residence in the south and injection-related risk behavior might identify specific place-based features that sustain patterns of injection-related risk behavior.

Reduction in Needle Sharing Among Seattle-Area Injection Drug Users Across 4 Surveys, 1994-2013

OBJECTIVES

We evaluated time trends in sharing needles and other injection equipment from 1994 to 2013 among injection drug users in the Seattle, Washington area.

METHODS

We combined data from 4 sources: the Risk Activity Variables, Epidemiology, and Network (RAVEN) study, recruited from institutional settings; the Kiwi study, recruited from jails; National HIV Behavioral Surveillance system (NHBS) surveys, which used respondent-driven sampling; and surveys at needle-exchange sites.

RESULTS

Levels of needle sharing were higher in the earlier studies: RAVEN, 1994 to 1997 (43%) and Kiwi, 1998 to 2002 (61%). In the NHBS surveys, the initial level of 44% in 2005 declined to 31% in the period 2009 to 2012. Across needle-exchange surveys (2009-2013) the level was 21%. There was a parallel reduction in sharing other injection equipment. These trends persisted after control for sociodemographic and risk-associated variables. There was a contemporaneous increase in the number of needles distributed by local needle exchanges and a decline in the number of reported HIV cases among injection drug users.

CONCLUSIONS

The apparent long-term reduction in sharing injection equipment suggests substantial success in public health efforts to reduce the sharing of injection equipment.

HIV Infection Among People Who Inject Drugs in the United States: Geographically Explained Variance Across Racial and Ethnic Groups

OBJECTIVES

We explored how variance in HIV infection is distributed across multiple geographical scales among people who inject drugs (PWID) in the United States, overall and within racial/ethnic groups.

METHODS

People who inject drugs (n = 9077) were recruited via respondent-driven sampling from 19 metropolitan statistical areas (MSAs) for the Centers for Disease Control and Prevention's 2009 National HIV Behavioral Surveillance system. We used multilevel modeling to determine the percentage of variance in HIV infection explained by zip codes, counties, and MSAs where PWID lived, overall and for specific racial/ethnic groups.

RESULTS

Collectively, zip codes, counties, and MSAs explained 29% of variance in HIV infection. Within specific racial/ethnic groups, all 3 scales explained variance in HIV infection among non-Hispanic/Latino White PWID (4.3%, 0.2%, and 7.5%, respectively), MSAs explained variance among Hispanic/Latino PWID (10.1%), and counties explained variance among non-Hispanic/Latino Black PWID (6.9%).

CONCLUSIONS

Exposure to potential determinants of HIV infection at zip codes, counties, and MSAs may vary for different racial/ethnic groups of PWID, and may reveal opportunities to identify and ameliorate intraracial inequities in exposure to determinants of HIV infection at these geographical scales.

Brief Report: Respondent-driven Sampling Estimators Under Real and Theoretical Recruitment Conditions of Female Sex Workers in China

We compare the performance of multiple respondent-driven sampling estimators under different sample recruitment conditions in hidden populations of female sex workers in the midst of China's ongoing epidemic of sexually transmitted infections. We first examine empirically calibrated simulations grounded in survey data to evaluate the relative performance of each estimator under ideal sampling conditions consistent with respondent-driven sampling assumptions and under conditions that mimic observed respondent-driven sampling recruitment processes. One estimator, which incorporates respondents' reports on their network of contacts, substantially out-performs the others under all conditions. We then apply the estimators to empirical samples of female sex workers collected in two Chinese cities that include unique data on respondents' networks. These empirical results are consistent with the simulation results, suggesting that traditional respondent-driven sampling estimators overestimate the proportion of female sex workers working in low tiers of sex work and are likely to overstate the sexually transmitted infection risk profiles of these populations.

HIV, STI and Behavioral Risk Among Men Who have Sex with Men in a Setting of Elevated HIV Prevalence Along Ecuador's Pacific Coast

We assessed HIV and STI prevalence, risk behaviors and factors associated with HIV infection in men who have sex with men (MSM) in Guayaquil, Ecuador. Respondent-driven sampling was used to recruit 400 MSM in 2011-2012. Participants completed a computer-assisted self-interview and provided blood samples. Statistical analysis accounted for differential probability of selection and for recruitment patterns. HIV prevalence was 11.3 %, HSV-2 30.2 %, active syphilis 6.9 % and hepatitis B 1.2 %. In the previous 12 months, 84 % of MSM reported casual male sex partners and 25 % sex work. Only 48 % of MSM consistently used condoms with male partners and 54 % had ever been tested for HIV. Of 17 % of MSM reporting a female partner, consistent condom use was 6 %. HIV infection was associated with age 25 or older, active syphilis and homosexual self-identification. Findings suggest continuing HIV risk and a need to strengthen prevention and testing among MSM.

Heroin-related overdose: The unexplored influences of markets, marketing and source-types in the United States

Heroin overdose, more accurately termed 'heroin-related overdose' due to the frequent involvement of other drugs, is the leading cause of mortality among regular heroin users. (Degenhardt et al., 2010) Heroin injectors are at greater risk of hospital admission for heroin-related overdose (HOD) in the eastern United States where Colombian-sourced powder heroin is sold than in the western US where black 'tar' heroin predominates. (Unick et al., 2014) This paper examines under-researched influences on HOD, both fatal and non-fatal, using data from a qualitative study of injecting drug users of black tar heroin in San Francisco and powder heroin in Philadelphia Data were collected through in-depth, semi-structured interviews carried out in 2012 that were conducted against a background of longer-term participant-observation, ethnographic studies of drug users and dealers in Philadelphia (2007-12) and of users in San Francisco (1994-2007, 2012). Our findings suggest three types of previously unconsidered influences on overdose risk that arise both from structural socio-economic factors and from the physical properties of the heroin source-types: 1) retail market structure including information flow between users; 2) marketing techniques such as branding, free samples and pricing and 3) differences in the physical characteristics of the two major heroin source forms and how they affect injecting techniques and vascular health. Although chosen for their contrasting source-forms, we found that the two cities have contrasting dominant models of drug retailing: San Francisco respondents tended to buy through private dealers and Philadelphia respondents frequented an open-air street market where heroin is branded and free samples are distributed, although each city included both types of drug sales. These market structures and marketing techniques shape the availability of information regarding heroin potency and its dissemination among users who tend to seek out the strongest heroin available on a given day. The physical characteristics of these two source-types, the way they are prepared for injecting and their effects on vein health also differ markedly. The purpose of this paper is to examine some of the unexplored factors that may lead to heroin-related overdose in the United States and to generate hypotheses for further study.

Using Social Network as a Recruiting Tool for Research on Substance Use in the Taipei Metropolitan Area: Study Design, Implementation, and Epidemiological Estimates

Background

This study aimed to evaluate the practical utility of respondent-driven sampling (RDS) among regular tobacco and alcohol users in Taipei, Taiwan.

Methods

RDS was implemented from 2007 to 2010 to recruit seed individuals who were 18 to 50 years old, regular tobacco and alcohol users, and currently residing in Taipei. Each respondent was asked to refer up to five friends known to be regular tobacco smokers and alcohol drinkers to participate in the present study. Information pertaining to drug use was collected using an audio computer-assisted self-interview instrument. RDSAT software was used for data analyses.

Results

The prevalence estimates of illegal-drug-using behaviors attained equilibrium after three to five recruitment waves. Nearly one-fifth of the participants had ever used illegal drugs, of whom over 60% were polydrug users. The RDS-adjusted prevalences of illegal-drug-using behaviors among early-onset smokers were all two or three times higher than those among late-onset smokers.

Conclusions

Our results provided an empirical basis for the practicality and feasibility of using RDS to estimate illegal drug use prevalence among regular tobacco and alcohol users.

Examining the associations between sex trade involvement, rape, and symptomatology of sexual abuse trauma

The high prevalence of rape and sexual trauma symptomatology among women involved in street-based sex trades is well-established. Because prior research has lacked appropriate, non-sex trade involved comparison groups, it is unknown whether differences exist among similarly situated women who do and do not trade sex. This article explores experiences of childhood and adult rape and symptomatology of sexual abuse trauma among a community-based sample of 322 women who use methamphetamine in San Francisco, California, 61% of whom were involved in the sex trade. Study participants were recruited via respondent-driven sampling and eligible if they were cisgender women, aged 18 or older, current methamphetamine users, and sexually active with at least one cisgender man in the past 6 months. The dependent variable was sexual abuse trauma symptomatology, as measured by the Sexual Abuse Trauma Index (SATI) subscale of the Trauma Symptom Checklist-40 (TSC-40), and the explanatory variable was sex trade involvement. Potential covariates were age, current homelessness, methamphetamine dependence, and experiences of childhood and adult rape. Sixty-one percent of participants had a SATI subscale score suggestive of sexual abuse trauma. The overall prevalence of rape in childhood and adulthood was 52% and 73%, respectively. In bivariate analysis, sex trade involvement and all of the potential covariates except for homelessness and age were associated with a SATI score suggestive of sexual abuse trauma. In multivariate models controlling for significant covariates, there was no longer a statistically significant association between sex trade involvement or childhood rape and an elevated SATI score. Elevated levels of psychological dependence on methamphetamine and experiences of rape as an adult were still associated with a high SATI score. These findings highlight that urban poor women, regardless of sex trade involvement, suffer high levels of rape and related trauma symptomatology.

Assessing the geographic coverage and spatial clustering of illicit drug users recruited through respondent-driven sampling in New York City

We assess the geographic coverage and spatial clustering of drug users recruited through respondent-driven sampling (RDS) and discuss the potential for biased RDS prevalence estimates. Illicit drug users aged 18-40 were recruited through RDS (N = 401) and targeted street outreach (TSO) (N = 210) in New York City. Using the Google Maps API™, we calculated travel distances and times using public transportation between each participant's recruitment location and the study office and between RDS recruiter-recruit pairs. We used K function analysis to evaluate and compare spatial clustering of (1) RDS vs. TSO respondents and (2) RDS seeds vs. RDS peer recruits. All participant recruitment locations clustered around the study office; however, RDS participants were significantly more likely to be recruited within walking distance of the study office than TSO participants. The TSO sample was also less spatially clustered than the RDS sample, which likely reflects (1) the van's ability to increase the sample's geographic heterogeneity and (2) that more TSO than RDS participants were enrolled on the van. Among RDS participants, individuals recruited spatially proximal peers, geographic coverage did not increase as recruitment waves progressed, and peer recruits were not less spatially clustered than seeds. Using a mobile van to recruit participants had a greater impact on the geographic coverage and spatial dependence of the TSO than the RDS sample. Future studies should consider and evaluate the impact of the recruitment approach on the geographic/spatial representativeness of the sample and how spatial biases, including the preferential recruitment of proximal peers, could impact the precision and accuracy of estimates.

HIV prevalence and risk behaviors among people who inject drugs in two serial cross-sectional respondent-driven sampling surveys, Zanzibar 2007 and 2012

People who inject drugs (PWID) are at higher risk of acquiring HIV due to risky injection and sexual practices. We measured HIV prevalence and behaviors related to acquisition and transmission risk at two time points (2007 and 2012) in Zanzibar, Tanzania. We conducted two rounds of behavioral and biological surveillance among PWID using respondent-driven sampling, recruiting 499 and 408 PWID, respectively. Through faceto- face interviews, we collected information on demographics as well as sexual and injection practices. We obtained blood samples for biological testing. We analyzed data using RDSAT and exported weights into STATA for multivariate analysis. HIV prevalence among sampled PWID in Zanzibar was 16.0 % in 2007 and 11.3 % in 2012; 73.2 % had injected drugs for 7 years or more in 2007, while in the 2012 sample this proportion was 36.9 %. In 2007, 53.6 % reported having shared a needle in the past month, while in the 2012 sample, 29.1 % reported having done so. While 13.3 % of PWID in 2007 reported having been tested for HIV infection and received results in the past year, this proportion was 38.0 % in 2012. Duration of injection drug use for 5 years or more was associated with higher odds of HIV infection in both samples. HIV prevalence and indicators of risk and preventive behaviors among PWID in Zanzibar were generally more favorable in 2012 compared to 2007-a period marked by the scale-up of prevention programs focusing on PWID. While encouraging, causal interpretation needs to be cautious and consider possible sample differences in these two cross-sectional surveys. HIV prevalence and related risk behaviors persist at levels warranting sustained and enhanced efforts of primary prevention and harm reduction.

Evaluation of respondent-driven sampling in a study of urban young men who have sex with men

Evidence suggests that respondent-driven sampling (RDS) is an efficient approach to sampling among varied populations of adult men who have sex with men (MSM) both in the USA and abroad, although no studies have yet evaluated its performance among younger MSM, a population with a steep rise in HIV infection in recent years. Young MSM (YMSM) may differ in terms of their connectedness to other YMSM (e.g., due to evolving sexual identity, internalization of sexual minority stigma, and lack of disclosure to others) and mobility (e.g., due to parental monitoring) which may inhibit the sampling process. The aims of this study were to evaluate the efficiency and effectiveness of RDS-based sampling among young urban MSM and to identify factors associated with recruitment success. We hypothesized that demographic, social, behavioral, and network factors, including racial/ethnic minority status, homelessness (i.e., as an indicator of socioeconomic marginalization), HIV-positive status, substance use problems, gay community connectedness, and network size would be positively related to recruitment productivity, while sexual minority stigmatization, environmental barriers (e.g., parental monitoring), and meeting sex partners on the internet (i.e., virtual venue) would be negatively related to recruitment productivity. Between December 2009 and February 2013, we used RDS to recruit a sample of 450 YMSM, ages 16-20. Findings suggest that the use of RDS for sampling among YMSM is challenging and may not be feasible based on the slow pace of recruitment and low recruitment productivity. A large number of seeds (38 % of the sample, n = 172) had to be added to the sample to maintain a reasonable pace of recruitment, which makes use of the sample for RDS-based population estimates questionable. In addition, the prevalence of short recruitment chains and segmentation in patterns of recruitment by race/ethnicity further hamper the network recruitment process. Thus, RDS was not particularly efficient in terms of the rate of recruitment or effective in generating a representative sample. Hypotheses regarding factors associated with recruitment success were supported for network size and internalized stigma (but not other factors), suggesting that participants with larger network sizes or high levels of internalized stigma may have more and less success recruiting others, respectively.

Evaluating outcome-correlated recruitment and geographic recruitment bias in a respondent-driven sample of people who inject drugs in Tijuana, Mexico

Respondent-driven sampling's (RDS) widespread use and reliance on untested assumptions suggests a need for new exploratory/diagnostic tests. We assessed geographic recruitment bias and outcome-correlated recruitment among 1,048 RDS-recruited people who inject drugs (Tijuana, Mexico). Surveys gathered demographics, drug/sex behaviors, activity locations, and recruiter-recruit pairs. Simulations assessed geographic and network clustering of active syphilis (RPR titers ≥1:8). Gender-specific predicted probabilities were estimated using logistic regression with GEE and robust standard errors. Active syphilis prevalence was 7 % (crude: men = 5.7 % and women = 16.6 %; RDS-adjusted: men = 6.7 % and women = 7.6 %). Syphilis clustered in the Zona Norte, a neighborhood known for drug and sex markets. Network simulations revealed geographic recruitment bias and non-random recruitment by syphilis status. Gender-specific prevalence estimates accounting for clustering were highest among those living/working/injecting/buying drugs in the Zona Norte and directly/indirectly connected to syphilis cases (men: 15.9 %, women: 25.6 %) and lowest among those with neither exposure (men: 3.0 %, women: 6.1 %). Future RDS analyses should assess/account for network and spatial dependencies.

Assessing differences in groups randomized by recruitment chain in a respondent-driven sample of Seattle-area injection drug users

PURPOSE

Respondent-driven sampling (RDS) is a form of peer-based study recruitment and analysis that incorporates features designed to limit and adjust for biases in traditional snowball sampling. It is being widely used in studies of hidden populations. We report an empirical evaluation of RDS's consistency and variability, comparing groups recruited contemporaneously, by identical methods and using identical survey instruments.

METHODS

We randomized recruitment chains from the RDS-based 2012 National HIV Behavioral Surveillance survey of injection drug users in the Seattle area into two groups and compared them in terms of sociodemographic characteristics, drug-associated risk behaviors, sexual risk behaviors, human immunodeficiency virus (HIV) status and HIV testing frequency.

RESULTS

The two groups differed in five of the 18 variables examined (P ≤ .001): race (e.g., 60% white vs. 47%), gender (52% male vs. 67%), area of residence (32% downtown Seattle vs. 44%), an HIV test in the previous 12 months (51% vs. 38%). The difference in serologic HIV status was particularly pronounced (4% positive vs. 18%). In four further randomizations, differences in one to five variables attained this level of significance, although the specific variables involved differed.

CONCLUSIONS

We found some material differences between the randomized groups. Although the variability of the present study was less than has been reported in serial RDS surveys, these findings indicate caution in the interpretation of RDS results.

Non-partner violence against women who use drugs in San Francisco

This article examines non-partner violence among women who use methamphetamine (N = 322), recruited in an inner-city neighborhood of San Francisco. The combined prevalence of non-partner physical or sexual violence in the past 6 months was 28%, roughly equal to the prevalence of partner violence (26%). In multivariate analysis, factors associated with non-partner violence included frequent subsistence difficulty (adjusted odds ratio [AOR] = 2.43, 95% confidence interval [CI] = [1.3, 4.6]) and sex trade (AOR = 2.27, 95% CI = [1.4, 4.1]). Having a steady male partner was not protective against non-partner violence. Violence perpetrated by non-partners should be considered when assessing social and structural factors that influence women's health.

Respondent driven sampling is an effective method for engaging methamphetamine users in HIV prevention research in South Africa

BACKGROUND

South Africa, in the midst of the world's largest HIV epidemic, has a growing methamphetamine problem. Respondent driven sampling (RDS) is a useful tool for recruiting hard-to-reach populations in HIV prevention research, but its use with methamphetamine smokers in South Africa has not been described. This study examined the effectiveness of RDS as a method for engaging methamphetamine users in a Cape Town township into HIV behavioral research.

METHODS

Standard RDS procedures were used to recruit active methamphetamine smokers from a racially diverse peri-urban township in Cape Town. Effectiveness of RDS was determined by examining social network characteristics (network size, homophily, and equilibrium) of recruited participants.

RESULTS

Beginning with eight seeds, 345 methamphetamine users were enrolled over 6 months, with a coupon return rate of 67%. The sample included 197 men and 148 women who were racially diverse (73% Coloured, 27% Black African) and had a mean age of 28.8 years (SD=7.2). Social networks were adequate (mean network size >5) and mainly comprised of close social ties. Equilibrium on race was reached after 11 waves of recruitment, and after ≤3 waves for all other variables of interest. There was little to moderate preference for either in- or out-group recruiting in all subgroups.

CONCLUSIONS

Results suggest that RDS is an effective method for engaging methamphetamine users into HIV prevention research in South Africa. Additionally, RDS may be a useful strategy for seeking high-risk methamphetamine users for HIV testing and linkage to HIV care in this and other low resource settings.

Challenges to recruiting population representative samples of female sex workers in China using Respondent Driven Sampling

We explore the network coverage of a sample of female sex workers (FSWs) in China recruited through Respondent Drive Sampling (RDS) as part of an effort to evaluate the claim of RDS of population representation with empirical data. We take advantage of unique information on the social networks of FSWs obtained from two overlapping studies--RDS and a venue-based sampling approach (PLACE)--and use an exponential random graph modeling (ERGM) framework from local networks to construct a likely network from which our observed RDS sample is drawn. We then run recruitment chains over this simulated network to assess the assumption that the RDS chain referral process samples participants in proportion to their degree and the extent to which RDS satisfactorily covers certain parts of the network. We find evidence that, contrary to assumptions, RDS oversamples low degree nodes and geographically central areas of the network. Unlike previous evaluations of RDS which have explored the performance of RDS sampling chains on a non-hidden population, or the performance of simulated chains over previously mapped realistic social networks, our study provides a robust, empirically grounded evaluation of the performance of RDS chains on a real-world hidden population.

Spatial, temporal and relational patterns in respondent-driven sampling: evidence from a social network study of rural drug users

BACKGROUND

Respondent-driven sampling (RDS) has become a common tool for recruiting high-risk populations for HIV research. However, few studies have explored the influence of geospatial proximity and relationship-level characteristics on RDS recruitment, particularly among high-risk individuals residing in rural areas of the US.

METHODS

In a social network study of 503 drug users in rural Central Appalachia, interviewer-administered questionnaires were used to collect relationship-level data (eg, duration of relationship, frequency of communication, kinship, social/financial support, trust, drug use and sex) and residential location. Demographic and drug-use similarity were also evaluated. Residential data were geocoded and road distance (km) between participants and (1) their network members and (2) the study site were computed. Seasonal patterns were assessed using node-level analysis, and dyadic analyses were conducted using generalised linear mixed models. Adjusted ORs (AORs) and 95% CIs are reported.

RESULTS

Differences in distance to the study office by season and order of study entry were not observed (F=1.49, p=0.209 and β=0.074, p=0.050, respectively). Participants with transportation lived significantly further from the interview site than their counterparts (p<0.001). Dyadic analyses revealed no association between RDS recruitment likelihood and geographic proximity. However, kinship (AOR 1.62; CI 1.02 to 2.58) and frequency of communication (AOR 1.63; CI 1.25 to 2.13) were significantly associated with RDS recruitment.

CONCLUSIONS

In this sample, recruitment from one's network was likely non-random, contradicting a core RDS assumption. These data underscore the importance of formative research to elucidate potential recruitment preferences and of quantifying recruitment preferences for use in analysis.

Using the National HIV Behavioral Surveillance System to inform HIV prevention efforts in the United States

The National HIV Behavioral Surveillance system (NHBS) was designed to monitor HIV prevalence and risk factors for infection among higher-risk individuals, i.e., sexually active men who have sex with men who attend venues, injection drug users who injected in the past 12 months, and heterosexuals living in low socioeconomic urban areas. These groups were selected as priorities for behavioral surveillance since they represent the major HIV transmission routes and the populations with the highest HIV burden. NHBS contributes to the nation's program of HIV surveillance by being the only multi-site population-based system that provides estimates on key HIV prevention measures among high-risk HIV-negative individuals, HIV-positive individuals unaware of their infection, and HIV-positive individuals aware of their infection who are in and out of care. Accurate and precise data on the behaviors in these populations are critical for tracking the epidemic, planning effective responses, and monitoring and evaluating those responses. Reports in this supplement illustrate the uses of NHBS data at the national and local level and reflect ongoing efforts to improve the system and remains essential for characterizing and monitoring the burden of HIV infection and sexual and behavioral risks.

Unmet healthcare need among women who use methamphetamine in San Francisco

Methamphetamine use has increased substantially in the United States since the 1990s. Few studies have examined the healthcare service needs of women who use methamphetamine. This study describes unmet medical needs in a community-based sample of women who use methamphetamine in San Francisco, CA. Women who use methamphetamine were recruited in San Francisco and participated in a computer-assisted survey (N = 298 HIV-negative women). Multivariate analysis was performed to explore associations among sociodemographic variables, drug use, use of health and social services, and unmet healthcare need across three domains: chronic health problems, dermatologic problems, and women's preventive healthcare. Sixty-nine percent of participants reported a need for care for a chronic health condition, and 31% of them had an unmet need for care, in the last six months. Thirty-five percent of participants reported a need for dermatologic healthcare, and 66% had an unmet need for care in the last 6 months. Ninety-two percent of participants reported a need for women's preventive healthcare and 46% had an unmet need for care in the last year. Women who reported having a healthcare provider had lower odds of reporting an unmet need for a chronic health condition or women's preventive healthcare. Women who used a case manager had lower odds of having an unmet need for dermatologic care. A significant proportion of women who use methamphetamine in this sample had an unmet need for women's preventive healthcare, and overall these women had a significant unmet need for healthcare. These findings suggest that contact with a healthcare provider or a caseworker could help to expand access to healthcare for this vulnerable population.

Patterns and predictors of multiple sexual partnerships among newly arrived Latino migrant men

Multiple sexual partnerships (MSP), both concurrent and serial short gap, are thought to increase the risk of HIV and sexually transmitted infection (STI) acquisition and transmission. In this study we evaluate potential individual and environmental risk factors for engaging in MSP in a cohort of newly arrived Latino migrant men (LMM) in New Orleans, LA, USA. Participants were surveyed at three time points over a nine-month period to examine factors associated with MSP. Of the 113 men, 32.5 % reported ever MSP. In 290 observations, 19.5 % of men had concurrent, and 15.0 % had serial short gap partnerships in at least one interviews. Substance was associated with MSP, OR (95 % CI) 2.00 (1.16, 3.45) whereas belonging to a community organization was found to be protective, OR 0.32 (0.17, 0.59). Interventions to reduce substance use and promote social connection are needed to prevent a potential HIV/STI epidemic in this population.

Seroadaptation in a sample of very poor Los Angeles area men who have sex with men

Data from 635 very poor men who have sex with men (MSM) were used to identify seroadaptation with 1,102 male partners reported between 2005 and 2007 in Los Angeles as part of the Sexual Acquisition and Transmission of HIV Cooperative Agreement Program. The mean age of the sample was 41.7 years; 53 % had experienced homelessness in the past year. Condoms were reported in 51 % of sexual events involving anal intercourse. HIV seroconcordance was reported in 41 % of sexual partnerships among HIV-positive participants. HIV-positive men were more likely to have oral-only or unprotected receptive anal intercourse and less likely to have unprotected insertive anal intercourse with HIV-negative or unknown partners compared to HIV-positive partners. Even in the face of poverty, HIV-positive MSM report mitigating risks of HIV-transmission though seroadaptation in the context of modest rates of condom use.

Differing HIV risks and prevention needs among men and women injection drug users (IDU) in the District of Columbia

Washington, DC has among the highest HIV/AIDS rates in the US. Gender differences among injection drug users (IDUs) may be associated with adoption of prevention opportunities including needle exchange programs, HIV testing, psychosocial support, and prevention programming. National HIV Behavioral Surveillance data on current IDUs aged ≥18 were collected from 8/09 to 11/09 via respondent-driven sampling in Washington, DC. HIV status was assessed using oral OraQuick with Western Blot confirmation. Weighted estimates were derived using RDSAT. Stata was used to characterize the sample and differences between male and female IDU, using uni-, bi-, and multivariable methods. Factors associated with HIV risk differed between men and women. Men were more likely than women to have had a history of incarceration (86.6 % vs. 66.8 %, p < 0.01). Women were more likely than men to have depressive symptoms (73.9 % vs. 47.4 %, p < 0.01), to have been physically or emotionally abused (66.1 % vs. 16.1 %, p < 0.0001), to report childhood sexual abuse (42.7 % vs. 4.7 %, p < 0.0001), and pressured or forced to have sex (62.8 % vs. 4.0 %, p < 0.0001); each of these differences was significant in the multivariable analysis. Despite a decreasing HIV/AIDS epidemic among IDU, there remain significant gender differences with women experiencing multiple threats to psychosocial health, which may in turn affect HIV testing, access, care, and drug use. Diverging needs by gender are critical to consider when implementing HIV prevention strategies.

A comparison of respondent-driven and venue-based sampling of female sex workers in Liuzhou, China

Objectives

To compare two methods for sampling female sex workers (FSWs) for bio-behavioural surveillance. We compared the populations of sex workers recruited by the venue-based Priorities for Local AIDS Control Efforts (PLACE) method and a concurrently implemented network-based sampling method, respondent-driven sampling (RDS), in Liuzhou, China.

Methods

For the PLACE protocol, all female workers at a stratified random sample of venues identified as places where people meet new sexual partners were interviewed and tested for syphilis. Female workers who reported sex work in the past 4 weeks were categorised as FSWs. RDS used peer recruitment and chain referral to obtain a sample of FSWs. Data were collected between October 2009 and January 2010. We compared the socio-demographic characteristics and the percentage with a positive syphilis test of FSWs recruited by PLACE and RDS.

Results

The prevalence of a positive syphilis test was 24% among FSWs recruited by PLACE and 8.5% among those recruited by RDS and tested (prevalence ratio 3.3; 95% CI 1.5 to 7.2). Socio-demographic characteristics (age, residence and monthly income) also varied by sampling method. PLACE recruited fewer FSWs than RDS (161 vs 583), was more labour-intensive and had difficulty gaining access to some venues. RDS was more likely to recruit from areas near the RDS office and from large low prevalence entertainment venues.

Conclusions

Surveillance protocols using different sampling methods can obtain different estimates of prevalence and population characteristics. Venue-based and network-based methods each have strengths and limitations reflecting differences in design and assumptions. We recommend that more research be conducted on measuring bias in bio-behavioural surveillance.

Respondent-driven sampling in a syringe exchange setting

Aims: Respondent-driven sampling is a research technique, new to the Scandinavian setting, used in hard-to-reach populations, such as subjects at risk for HIV, including drug users. This study aimed to evaluate the use of respondent-driven sampling originating from syringe exchange clients, as a method to identify ‘hidden’ drug users without treatment or social service contact. Methods: Nine heroin and amphetamine injectors were recruited as ‘seeds’ and instructed to recruit up to three heavy drug users in a chain-referral process. Recruited clients were interviewed about drug use, social conditions and contacts with treatment, syringe exchange and other authorities. In order to estimate whether the recruitment managed to evolve into groups of ‘hidden’ drug users, clients included beyond the fourth wave of chain-referral were compared with seeds (wave 0) and clients recruited in waves 1–3. Results: Five seeds were generative, and in total, 66 clients were assessed. Except for one of the 35 variables studied, clients in waves 4–9 did not differ from clients in waves 0–3, and were no less likely to have contacts with authorities. All clients except one were injectors and syringe exchangers, and clients recruited later in the chain-referral even tended to attend the syringe exchange more frequently. Conclusions: Respondent-driven sampling originating from syringe exchange clients may have difficulty reaching beyond the population of injectors and syringe exchangers. The technique, new to this geographical setting, has potential for future studies, but particular efforts may be necessary to study out-of-treatment heavy drug users unknown to the syringe exchange program.

Understanding the HIV/AIDS epidemic in transgender women of Lima, Peru: results from a sero-epidemiologic study using respondent driven sampling

In Latin America, transgender women (transwomen or male to female transgenders) have been included in MSM research but without addressing their specific needs in terms of the HIV/AIDS. We present results of the first seroepidemiologic study designed for transwomen in Peru. We conducted a study using respondent driven sampling to recruit transwomen from Lima. Our survey explored sociodemographic characteristics, gender enhancement procedures and sexual behavior. In addition, we conducted laboratory based HIV, genital herpes (HSV2) and syphilis testing. A total of 450 transwomen were recruited between April and July 2009. HIV prevalence was 30%, HSV2: 79% and syphilis: 23%. Sex-work was the main economic activity (64%). Gender enhancement procedures were reported by 70% of the population. Multivariable analysis showed HIV infection to be associated with being older than 35 recent, syphilis infection and HSV2 infection. Transwomen are the group most vulnerable to HIV/AIDS in Peru.

Respondent-driven sampling and the recruitment of people with small injecting networks

Respondent-driven sampling (RDS) is a form of chain-referral sampling, similar to snowball sampling, which was developed to reach hidden populations such as people who inject drugs (PWID). RDS is said to reach members of a hidden population that may not be accessible through other sampling methods. However, less attention has been paid as to whether there are segments of the population that are more likely to be missed by RDS. This study examined the ability of RDS to capture people with small injecting networks. A study of PWID, using RDS, was conducted in 2009 in Sydney, Australia. The size of participants' injecting networks was examined by recruitment chain and wave. Participants' injecting network characteristics were compared to those of participants from a separate pharmacy-based study. A logistic regression analysis was conducted to examine the characteristics independently associated with having small injecting networks, using the combined RDS and pharmacy-based samples. In comparison with the pharmacy-recruited participants, RDS participants were almost 80% less likely to have small injecting networks, after adjusting for other variables. RDS participants were also more likely to have their injecting networks form a larger proportion of those in their social networks, and to have acquaintances as part of their injecting networks. Compared to those with larger injecting networks, individuals with small injecting networks were equally likely to engage in receptive sharing of injecting equipment, but less likely to have had contact with prevention services. These findings suggest that those with small injecting networks are an important group to recruit, and that RDS is less likely to capture these individuals.

Evaluation of respondent-driven sampling

BACKGROUND

Respondent-driven sampling is a novel variant of link-tracing sampling for estimating the characteristics of hard-to-reach groups, such as HIV prevalence in sex workers. Despite its use by leading health organizations, the performance of this method in realistic situations is still largely unknown. We evaluated respondent-driven sampling by comparing estimates from a respondent-driven sampling survey with total population data.

METHODS

Total population data on age, tribe, religion, socioeconomic status, sexual activity, and HIV status were available on a population of 2402 male household heads from an open cohort in rural Uganda. A respondent-driven sampling (RDS) survey was carried out in this population, using current methods of sampling (RDS sample) and statistical inference (RDS estimates). Analyses were carried out for the full RDS sample and then repeated for the first 250 recruits (small sample).

RESULTS

We recruited 927 household heads. Full and small RDS samples were largely representative of the total population, but both samples underrepresented men who were younger, of higher socioeconomic status, and with unknown sexual activity and HIV status. Respondent-driven sampling statistical inference methods failed to reduce these biases. Only 31%-37% (depending on method and sample size) of RDS estimates were closer to the true population proportions than the RDS sample proportions. Only 50%-74% of respondent-driven sampling bootstrap 95% confidence intervals included the population proportion.

CONCLUSIONS

Respondent-driven sampling produced a generally representative sample of this well-connected nonhidden population. However, current respondent-driven sampling inference methods failed to reduce bias when it occurred. Whether the data required to remove bias and measure precision can be collected in a respondent-driven sampling survey is unresolved. Respondent-driven sampling should be regarded as a (potentially superior) form of convenience sampling method, and caution is required when interpreting findings based on the sampling method.

Evaluating consistency in repeat surveys of injection drug users recruited by respondent-driven sampling in the Seattle area: results from the NHBS-IDU1 and NHBS-IDU2 surveys

PURPOSE

We compared data from two respondent-driven sampling (RDS) surveys of Seattle-area injection drug users (IDU) to evaluate consistency in repeat RDS surveys.

METHODS

The RDS-adjusted estimates for 16 key sociodemographic, drug-related, sexual behavior, and HIV- and hepatitis C virus-related variables were compared in the 2005 and the 2009 National HIV Behavioral Surveillance system surveys (NHBS-IDU1 and NHBS-IDU2). Time trends that might influence the comparisons were assessed by the use of data from reported HIV cases in IDU, surveys of needle exchange users, and two previous IDU studies.

RESULTS

NHBS-IDU2 participants were more likely than NHBS-IDU1 participants to report older age, heroin as their primary injection drug, male-to-male sex, unprotected sex with a partner of nonconcordant HIV status, and to self-report HIV-positive status. NHBS-IDU2 participants were less likely to report residence in downtown Seattle, amphetamine injection, and a recent HIV test. Time trends among Seattle-area IDU in age, male-to-male sex, and HIV testing could have influenced these differences.

CONCLUSIONS

The number and magnitude of the estimated differences between the two RDS surveys appeared to describe materially different populations. This could be a result of changes in the characteristics of Seattle-area IDU over time, of accessing differing subpopulations of Seattle IDU, or of high variability in RDS measurements.

Respondent-driven sampling to recruit young adult non-medical users of pharmaceutical opioids: problems and solutions

Respondent-driven sampling (RDS) has been promoted as a superior method in recruiting hard-to-reach and hidden populations. Although its application has expanded enormously, there remains a need for empirical data evaluating the performance of RDS in different settings. This study describes the application of RDS to recruit a community sample (N=396) of young adults (18-23 years old) into a natural history study of non-medical pharmaceutical opioid use. Since recruitment targeted non-dependent pharmaceutical opioid users, and applied other eligibility restrictions, several modifications had to be made to make RDS work with this narrowly defined target population. RDS recruitment was less efficient than expected, and produced greater numbers of African American recruits than anticipated. Although the sampling quota was met, sample analysis revealed a lack of equilibrium in terms of ethnic composition and very strong in-group recruitment tendencies among White and African American respondents. This study contributes potentially helpful insights into the strengths and limitations of using RDS which may benefit future studies.

Differential profiles of crack users in respondent-driven and institutional samples: a three-site comparison

BACKGROUND/AIM

Respondent-driven sampling (RDS) is increasingly applied in social epidemiological surveys among 'hidden populations' of hard drug users. The objective of the present study was to assess whether the profile of frequent crack users recruited through RDS differed from those surveyed in two random institutional samples, i.e. low-threshold opiate substitution treatment (ST) and user rooms (URs).

METHODS

A total of 1,039 crack users (mean age 45.1 ± 9.1 years; 81.5% males; 49.5% non-Western ethnicity) were interviewed in three Dutch cities, using each sampling strategy in each city. Characteristics of respondents in the three samples (per city and aggregated) were compared.

RESULTS

Crack users in the RDS sample were more likely to be younger and less likely to be poorly educated, have a long crack-using career (≥10 years), use opiates and attend ST than those in both of the other samples. The RDS and UR samples showed the most differences, with more female and Western crack users in the RDS group, and UR participants were more likely to have been arrested and to have entered inpatient drug treatment in the last year.

CONCLUSION

RDS resulted in a different profile of crack users. It is a valuable methodology to achieve a more diverse representation of crack-using populations than institutional random samples.

Evaluation of the role of location and distance in recruitment in respondent-driven sampling

BACKGROUND

Respondent-driven sampling(RDS) is an increasingly widely used variant of a link tracing design for recruiting hidden populations. The role of the spatial distribution of the target population has not been robustly examined for RDS. We examine patterns of recruitment by location, and how they may have biased an RDS study findings.

METHODS

Total-population data were available on a range of characteristics on a population of 2402 male household-heads from an open cohort of 25 villages in rural Uganda. The locations of households were known a-priori. An RDS survey was carried out in this population, employing current RDS methods of sampling and statistical inference.

RESULTS

There was little heterogeneity in the population by location. Data suggested more distant contacts were less likely to be reported, and therefore recruited, but if reported more distant contacts were as likely as closer contacts to be recruited. There was no evidence that closer proximity to a village meeting place was associated with probability of being recruited, however it was associated with a higher probability of recruiting a larger number of recruits. People living closer to an interview site were more likely to be recruited.

CONCLUSIONS

Household location affected the overall probability of recruitment, and the probability of recruitment by a specific recruiter. Patterns of recruitment do not appear to have greatly biased estimates in this study. The observed patterns could result in bias in more geographically heterogeneous populations. Care is required in RDS studies when choosing the network size question and interview site location(s).

Correlates of risky injection practices among past-year injection drug users among the US general population

BACKGROUND

With an estimated 1 million active injection drug users (IDUs), injection drug use continues to be a public health concern in the United States. Risky injection practices have been associated with the transmission of HIV, Hepatitis B and C, as well as other skin and soft tissue infections.

METHODS

We used data from 463 respondents, aged 18 and older, who were past-year IDUs in the 2005-2008 National Survey of Drug Use and Health (NSDUH). We investigated correlates of risky injection behavior among these recent IDUs.

RESULTS

Older age (≥ 35 versus 18-25) was associated with reusing one's own needle at last injection (aOR=1.80 [1.02-3.17], as were past year heroin (aOR=2.59 [1.18-5.66]) and cocaine injection (aOR=2.17 [1.13-4.15]). Past year crack cocaine use was positively associated with not cleaning needles with bleach (aOR=2.18 [1.10-4.33]). Past year cocaine injection was associated with obtaining needles in a risky manner (aOR=2.29 [1.23-4.25]). Methamphetamine injection was associated with obtaining needles in less risky ways (aOR=0.41 [0.20-0.84]).

CONCLUSION

Our findings indicate that some IDUs are continuing to engage in high risk injection behaviors. The identification of potential at-risk populations of IDUs may have implications for harm reduction interventions and HIV prevention programs.

Subpopulations of illicit drug users reached by targeted street outreach and respondent-driven sampling strategies: implications for research and public health practice

PURPOSE

To determine whether illicit drug users recruited through respondent-driven sampling (RDS) and targeted street outreach (TSO) differ by comparing two samples recruited concurrently with respect to sample selection and potential recruitment biases.

METHODS

Two hundred seventeen (217) heroin, crack, and cocaine users aged 18-40 years were recruited through TSO in New York City (2006-2009). Forty-six RDS seeds were recruited similarly and concurrently, yielding a maximum of 14 recruitment waves and 357 peer recruits. Baseline questionnaires ascertained sociodemographic, drug use, and drug network characteristics. Descriptive statistics and log-binomial regression were used to compare RDS and TSO samples.

RESULTS

RDS recruits were more likely to be male (prevalence ratio [PR]:1.28), Hispanic (PR:1.45), black (PR: 1.58), older (PR: 1.02), homeless (PR: 1.19), and crack users (PR: 1.37). RDS recruited fewer injectors (PR:0.35) and heroin users (PR:0.74). Among injectors, RDS recruits injected less frequently (PR:0.77) and were less likely to use Needle Exchange Programs (PR:0.35).

CONCLUSION

These data suggest that RDS and TSO strategies reach different subgroups of drug users. Understanding the differing capabilities of each recruitment strategy will enable researchers and public health practitioners to select an appropriate recruitment tool for future research and public health practice.

Cannabis Dependence and Peer Selection in Social Networks of Frequent Users

In a Dutch longitudinal study on the dynamics of cannabis dependence, at baseline 600 frequent cannabis users (? 3 days cannabis use per week in past 12 months) aged 18–30 years were interviewed. Nearly half of all participants (42%) met DSM-IV criteria for cannabis dependence in the 12 months prior to the interview. Participants were recruited by respondent-driven sampling; referrals were understood as proxy for social networks to explore peer associations and social exclusion. Analyses revealed that networks of frequent cannabis users were mostly heterogeneous. Cannabis dependence did not emerge as a main selector. However, within segments of networks some clustering of cannabis dependence (indicating differential inclusion), sex and ethnicity was found. Methodological questions are discussed regarding the applicability of respondent-driven sampling in noninjecting, nonmarginalized drug users. The study's limitations are noted.

Assessing respondent-driven sampling

Respondent-driven sampling (RDS) is a network-based technique for estimating traits in hard-to-reach populations, for example, the prevalence of HIV among drug injectors. In recent years RDS has been used in more than 120 studies in more than 20 countries and by leading public health organizations, including the Centers for Disease Control and Prevention in the United States. Despite the widespread use and growing popularity of RDS, there has been little empirical validation of the methodology. Here we investigate the performance of RDS by simulating sampling from 85 known, network populations. Across a variety of traits we find that RDS is substantially less accurate than generally acknowledged and that reported RDS confidence intervals are misleadingly narrow. Moreover, because we model a best-case scenario in which the theoretical RDS sampling assumptions hold exactly, it is unlikely that RDS performs any better in practice than in our simulations. Notably, the poor performance of RDS is driven not by the bias but by the high variance of estimates, a possibility that had been largely overlooked in the RDS literature. Given the consistency of our results across networks and our generous sampling conditions, we conclude that RDS as currently practiced may not be suitable for key aspects of public health surveillance where it is now extensively applied.