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The street cost of drugs and drug use patterns : relationships with sex work income in an urban Canadian… Deering, Kathleen N.; Shoveller, Jean; Tyndall, Mark; Montaner, Julio; Shannon, Kate Nov 30, 2011

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THE STREET COST OF DRUGS AND DRUG USE PATTERNS:RELATIONSHIPS WITH SEX WORK INCOME IN AN URBANCANADIAN SETTINGKN Deering1,2, J Shoveller2, MW Tyndall3, JS Montaner1,4, and K Shannon1,2,41British Columbia Centre for Excellence in HIV/AIDS, St. Paul’s Hospital, 608-1081 BurrardStreet, Vancouver, BC, CANADA, V6Z 1Y62School of Population and Public Health, University of British Columbia, 5804 Fairview Avenue,Vancouver, BC, CANADA, V6T 1Z33Division of Infectious Diseases, Faculty of Medicine, University of Ottawa 501 Smyth Road,Ottawa, ON, CANADA K1H 8L64Department of Medicine, University of British Columbia, St. Paul’s Hospital, 608-1081 BurrardStreet, Vancouver, BC, CANADA, V6Z 1Y6AbstractBackground—This study investigated the relationship between drug use and sex work patternsand sex work income earned among street-based female sex workers (FSWs) in Vancouver,Canada.Methods—We used data from a sample of 129 FSWs who used drugs in a prospectivec cohort(2007–2008), for a total of 210 observations. Bivariate and multivariable linear regression usinggeneralized estimating equations was used to model the relationship between explanatory factorsand sex work income. Sex work income was log-transformed to account for skewed data.Results—The median age of the sample at first visit was 37 years (interquartile range[IQR]: 30–43), with 46.5% identifying as Caucasian, 48.1% as Aboriginal and 5.4% as another visibleminority. The median weekly sex work income and amount spent on drugs was $300 (IQR =$100–$560) and $400 (IQR = $150–$780), respectively. In multivariable analysis, for a 10%increase in money spent on drugs, sex work income increased by 1.9% (coeff: 0.20, 95% CIs:0.04–0.36). FSWs who injected heroin, FSWs with higher numbers of clients and youth comparedto older women (<25 versus 25+ years) also had significantly higher sex work income.Conclusions—This study highlights the important role that drug use plays in contributing toincreased dependency on sex work for income among street-based FSWs in an urban Canadiansetting, including a positive dose-response relationship between money spent on drugs and sexwork income. These findings indicate a crucial need to scale up access and availability ofevidence-based harm reduction and treatment approaches, including policy reforms, improvedsocial support and economic choice for vulnerable women.Keywordssex workers; drug use; income; addiction treatment; harm reduction; evidence-based policiesContributors: KD and KS contributed to the conceptual design of the article and analyses plan. KD conducted all statistical analysesand prepared the initial draft. All other authors provided content expertise and critical feedback on the paper.Conflict of interest: All of the authors declare that they have no conflicts of interest.NIH Public AccessAuthor ManuscriptDrug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.Published in final edited form as:Drug Alcohol Depend. 2011 November 1; 118(2-3): 430–436. doi:10.1016/j.drugalcdep.2011.05.005.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscript1. INTRODUCTIONLike many other occupations, sex work is conducted primarily for economic gain. There areobvious differences that separate sex work from other occupations, including the increasedrisks to sexual health and safety, social and economic vulnerability and a high degree ofmarginalization and criminalization in many settings (Blanchard et al., 2005, Dandona et al.,2006, Rekart, 2005, Shannon et al., 2008a and Strathdee et al., 2008). The socialstigmatization (Della Guista et al., 2005 and Scambler and Paoli, 2008) and lack of legalregulation (Hubbard et al., 2008 and Letheby et al., 2008) are arguably among the maincharacteristics of sex work that separate it from other professions in which bodily services(e.g., massage) are provided.The vulnerability of women in sex work to sex work-related harms including high rates ofsexually transmitted infections (STIs) and HIV, violence and poverty, and marginalizationand isolation from health and social services has been well-documented (Rekart, 2005).A high concentration of harms has consistently been found in settings where street-based sexwork and drug markets coexist (Cusick, 2006, Harcourt et al., 2001, Harcourt and Donovan,2005, Lowman, 2000, Pyett and Warr, 1997, Rekart, 2005 and Shannon et al., 2008a). Druguse has been found to be an important antecedent to entry into street-based sex work forwomen (Malta et al., 2008 and Weber et al., 2004), including early initiation into sex work(Loza et al., 2010) and engaging in sex work for survival (Chettiar et al., 2010 and DeBecket al., 2007). Qualitative and ethnographic studies have documented that many womendepend on income from sex work to sustain drug use or to gain access to other commoditiessuch as food and shelter (Aral and St. Lawrence, 2002, Shannon et al., 2007, Shannon et al.,2008a and Strathdee et al., 2008). A dependence on sex work for income in the context ofdrug use can have a substantial impact on sex workers’ health, safety and well-being. femalesex workers (FSWs) who use drugs may earn less money than their non-drug-usingcounterparts, with increased pressures in negotiating prices due to immediacy of drugwithdrawal and need to sustain drug habit (Aral and St. Lawrence, 2002). Concurrently,FSWs who use drugs or with increased dependence on drugs may also be more susceptibleto agreeing to clients’ desires for sexual practices which can earn more money but carryhigher risk for HIV/STIs (e.g., having anal sex or not using condoms) (Aral and St.Lawrence, 2002). In many North American settings, the introduction of inexpensive andwidely available crack cocaine has been documented by women to result in being paid lessper sexual transaction, heightening their economic vulnerability (e.g., “$5 dates”) (Maher,2000 and Shannon et al., 2008a). Further, direct and indirect drug-sharing practices betweensex workers and clients have been shown to increase the likelihood of clients offering andworkers accepting more money for unprotected sex (Shannon et al., 2008a).Income earned from sex work reflects the numbers of sexual transactions that women havewith clients and the amount that women charge per client. A number of interpersonal andindividual factors may influence the amount charged, including the type of sex actperformed, the numbers of sex acts per client, the relationship with the client, condom useand characteristics of the sex worker (e.g., age, duration in sex work, work environment)(Gertler et al., 2005, Johnston et al., 2010, Rao et al., 2003 and Shannon et al., 2008a). Assuch, sex work income represents a complex set of factors measuring risk, vulnerability andeconomic dependence on sex work, particularly for those women who use drugs. Of the fewstudies that explore sex work earnings, most have focused on the economic costs to womenwhen they practice safer sex behaviour (e.g., the amount women could lose by refusing tonot use condoms), or have presented theoretical economic models describing howcompensation for sex work is linked with health and social costs (e.g., stigma, forgonemarriage opportunities, social exclusion, risks to health, safety and well-being) (CameronDeering et al. Page 2Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscriptand Collins, 2003, Della Giusta, 2010, Della Guista et al., 2005 and Edlund and Korn,2002).Despite the importance of drug use in influencing women’s initiation into and dependenceon sex work for income relative to those women who do not use drugs, comparatively fewerstudies have examined how the street cost of drugs, types of drug use and sex workcharacteristics independently relate to income earned by FSWs. The independentrelationship between the street cost of drugs and amount earned through sex work is ofparticular interest in this study, as assessing this relationship can quantify the acutevulnerability and susceptibility that sex workers who use drugs face within the context of thedrug market, and help contextualize the impact of structural-environmental factors affectingfluctuations in this market, including changes in drug prices, that are outside of their control.For example, police crackdowns that remove large quantities of drugs from drug marketscan result in a local increase in the street cost of drugs (Beyrer et al., 2010, Strathdee et al.,2010 and Wood et al., 2010). This analysis can also provide important insights into practicesof engaging in higher-risk behaviour in individual transactions in order for women to earnenough sex work income to still be able to afford drug use. Moreover, identifying drug useand sex work patterns associated with higher sex work income can point to groups ofindividuals who have a higher economic dependence on sex work to support their drug habitand who might benefit in particular from evidence-based harm reduction and treatmentapproaches. Therefore, we aimed to characterize the amount of money spent on drugs andearned through sex work by street-based FSWs who use drugs in Vancouver, Canada andexamine the drug use and sex work patterns associated with higher income earned from sexwork.2. METHODS2.1. Study design and sampleThis analysis is based on data from a prospective cohort of street-based sex workers as partof a community-based HIV prevention research partnership. A detailed description of themethodology is published elsewhere (Shannon et al., 2007). Briefly, between April, 2006and May, 2008, 255 women who were engaged in street-based sex work (inclusive oftransgendered women) were recruited and consented to participate in a prospective cohortstudy (response rate of 93%), including baseline and bi-annual questionnaires and voluntaryHIV screening, through systematic time-spacing sampling, social mapping and targetedoutreach to sex work strolls (Stueve et al., 2001). These street-based solicitation spaces wereidentified through a participatory mapping exercise conducted by current/former sexworkers. Eligibility criteria included being female or transgender aged 14 years or older whosmoked or injected illicit drugs (not including marijuana) in the past month and who wasactively engaged in street-level sex work in Vancouver. The study was approved through theProvidence Health Care Research Ethics Board and the University of British ColumbiaBehavioural Research Ethics Board.2.2. Survey instrumentAt baseline and follow-up visits (conducted every six months), a detailed questionnaireadministered face-to-face by peer researchers (i.e., current/former FSWs who were trainedand experienced in conducting community-based research) elicited responses related todemographics, health and addiction service use, working conditions, violence and safety,and sexual and drug-related harms. Data from this questionnaire has been used in manyother recent studies (Deering et al., 2010, Shannon et al., 2008b, Shannon et al., 2009a andShannon et al., 2009b).Deering et al. Page 3Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscript2.3. MeasuresThe primary outcome was average weekly sex work income earned, derived from the surveyitem, “Over the last 6 months, what were your main sources of income and how much didyou generate from each of these sources weekly?”We assessed multiple measures describing drug use and sex work patterns and theirrelationships with sex work income. These included the average weekly money spent ondrugs (derived from the item: “How much money do you think you spend on drugs in oneweek?”), which represents the street cost of drugs, and type of drug use (cocaine or heroininjection, and crystal methamphetamine injection/non-injection) during the past six months.Given the high rate of crack cocaine smoking in this population (Shannon et al., 2009a andShannon et al., 2009b), we also considered daily intensive crack smoking (≥10 versus <10times per day on average in the past six months). We also assessed the effects ofinterpersonal drug-related and sexual risk factors (e.g., receptive sharing of used syringesand/or pipes; having an intimate, non-commercial sexual partner; exchanging sex while highon crack cocaine; numbers of clients per week; condom use by clients in vaginal/anal sex;and being pressured by clients to not use condoms).Social factors considered included age (<25 years versus 25+ years) ethnicity (‘Caucasian’versus ‘ethnic minority’, including individuals of Aboriginal, First Nations, Metis, or Inuitancestry, Hispanic, Asian or Black). Based on previous research in Vancouver andelsewhere (Rhodes, 2002 and Shannon et al., 2009a), we derived two categories ofstructural/contextual variables: (1) Living environment and (2) Work environment. Livingenvironment was constructed as either homeless in the last six months (sleeping on the streetfor one night or more in the last six months versus not) or not homeless. Work environmentfactors included place of solicitation in the last six months (e.g., type of working area or sexwork stroll), including main street/commercial areas or alleys, side streets or industrialsettings, and place of servicing clients being primarily in indoor locations (e.g., hourlyrooms, saunas) or primarily outdoor locations (e.g., alleys, cars).We also adjusted for the amount of income earned through other sources, which includedgovernment-administered income (welfare, disability and nutrition supplements), legalinformal sources (binning, panhandling, partner’s income and under-the-table jobs), legalformal sources (temporary job, regular job) as well as non-legal sources (drug-related, e.g.,dealing). All monetary amounts were reported in Canadian dollars.2.4. Statistical analysisAs information on sex work income was only collected in follow-up questionnaires, thisanalysis was restricted to all participants who completed at least one follow-up visit(November 2007–October 2008). Social variables (age and ethnicity) reported at baselinewere considered as fixed variables. All other factors were treated as time-updated covariates(answered at each follow-up visit) that referred to experiences occurring during the previoussix-month period. As done previously (DeBeck et al., 2009, Richardson et al., 2008 andShannon et al., 2009b), to account for correlation between repeated measures for eachsubject (since women may have answered one or two surveys during this period, dependingon when they were enrolled), we used generalised estimating equations (GEEs) for theanalysis of correlated data; thus, data from each participant’s follow-up visit was included.GEE methods provided standard errors adjusted by repeated observations per person usingan exchangeable correlation structure. Missing data were addressed through the GEEestimating mechanism, which uses the all available pairs method to encompass the missingdata from dropouts or intermittent missing data. All non-missing pairs of data are used in theestimators of the working correlation parameters. All statistical analyses were performedDeering et al. Page 4Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscriptusing SAS software version 9.1 (2002–2003), (UCLA: Academic Technology Services,Statistical Consulting Group, n.d.).Bivariate and multivariable linear regression with GEEs was used to model the relationshipbetween drug use and sex work patterns and weekly sex work income earned. For use inlinear regression, sex work income, money spent on drugs, numbers of clients and otherincome earned were log-transformed to address highly skewed data. In order to adjust forpotential confounding, all variables that were significant on a p < 0.10 level in GEEbivariate analyses were entered in a multivariable linear GEE model. Variables wereretained as significant in the multivariable model with an alpha cut-off of p < 0.05. Bivariateand multivariable GEE regression coefficients and 95% confidence intervals (CIs) werecomputed and all p-values are two-sided. We reported percent increases in the regressioncoefficients.3. RESULTS3.1. Sample characteristicsOf the 255 participants enrolled in the prospective cohort, 167 women completed at leastone follow-up visit (mean = 2, range: 1–2 visits) in the 12-month period, and were thereforepotentially eligible for our analyses. Overall, 129 reported valid information on sex workincome at their first survey visit, providing a total of 210 (78.7%) observations for thisstudy. The median age of the 129 women at their first survey visit in this sample was 37years (interquartile range [IQR]: 30–43 years). Of this sample, 46.5% (60) of womenidentified as Caucasian, 48.1% (62) as Aboriginal and 5.4% (7) as another visible minority.Table 1 provides additional details for the sample at their first survey visit related to socialand environmental factors, drug use and sex work patterns. We compared women with andwithout valid responses to sex work income and found no significant differences betweenthe two samples in terms of age (pooled t-test: p = 0.71), ethnicity (Chi-squared test: p =0.07) and money spent on drugs (pooled t-test: p = 0.64).3.2. Sex work incomeIn a typical week, at their first survey visit, women reported earning a median of $300(mean: $500, IQR: $100–$560) from sex work income, spent a median of $400 (mean:$572, IQR: $150–$780) on drugs and had a median of 5.5 (mean: 11, IQR: 2–13) clients.Overall, 95% of women reported having some other income, earning a weekly median of$700 (mean: $780, IQR: $525–$1000) from this income. At their first survey visit, womenwho earned higher weekly sex work income were more likely to be younger (<25 versus25+ years), Caucasian, not currently homeless, inject heroin, inject cocaine, report intensivedaily crack smoking, not engage in receptive sharing of used pipes or syringes, always usecondoms with clients, exchanged sex while high on crack, solicit clients in main/commercialareas and not service clients in indoor establishments (Table 1). Fig. 1 describes therelationship between the log-transformed weekly amount spent on drugs and the log-transformed weekly sex work income earned. A best-fitting linear regression line depicts thelinear, positive relationship between the two variables.In bivariate linear regression with GEE for the total sample, age, heroin injection, cocaineinjective, intensive daily crack smoking, exchanging sex while high on crack, greaternumber of clients and the amount spent on drugs were significantly associated with highersex work income.Table 2 displays results from multivariable linear regression with GEEs. In multivariableanalysis, for a 10% increase in the amount of money spent on drugs, sex work incomeearned increased by 1.9% (coeff: 0.20, 95% CIs: 0.04–0.36). We also found that there was aDeering et al. Page 5Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscriptsignificant association between numbers of clients and sex work income earned, with a 10%increase in the numbers of clients associated with a 3.0% increase in sex work income(coeff: 0.32, 95% CIs: 0.19–0.42). In addition, women who were <25 years old compared tothose who were 25+ years reported significantly higher sex work income earned, withyounger women having a 43% increase in sex work income (coeff: 0.36, 95% CIs: 0.08–0.64) relative to older women. Women who injected heroin had a significant increase in sexwork income of 51% (coeff: 0.41, 95% CIs: 0.11–0.70) relative to women who did not.4. DISCUSSIONThis study examined the relationship between the street cost of drugs, drug use and sex workpatterns by street-based female sex workers in an urban Canadian setting. We found that in atypical week, women reported earning a median of $300 from sex work income, spent amedian of $400 on drugs and had a median of 6 clients. Overall, 95% of women reportedhaving some other income (including that from financial assistance, other legal employmentand illegal activities), earning a weekly median of $700 (mean = $780) from this income.The amount of money spent on drugs, heroin injection, numbers of clients and beingyounger (<25 versus 25+) were independently significantly associated with higher sex workincome in multivariate analysis.Our study is the first that we are aware of to empirically demonstrate an independent,positive dose-response relationship between the amount of money spent on drugs by womenin a street-based sex market and the amount of money they earn through sex work. This wasthe case even after adjusting for the type of drugs used and numbers of clients, indicatingthat another mechanism could be influencing the amount of income earned. Women whospend more on drugs may engage in sexual behaviour for which they can earn more moneyper transaction, including vaginal or anal sex as compared to oral sex. Many studies havesuggested that, due to constrained economic conditions, FSWs can be influenced by clients’demands to have sex without condoms in exchange for higher pay, including in our setting(Cusick, 1998, Johnston et al., 2010, Luke, 2006 and Shannon et al., 2008a). Of note, incontrast to this research, consistent condom use by clients was associated with higher sexwork income suggesting other dynamics may interact to shape the relationship betweencondom use by clients and weekly sex work income in street-based sex work economies,such as work environment and client population factors. The additional economic pressureof increased drug use (as represented by increased money spent on drugs, and thus the streetcost of drugs) may also influence sex worker’s vulnerability to engage in riskier behaviours(Strathdee et al., 2008). Although we adjusted for consistent condom use by clients, thiscannot capture the complexity of higher-risk transactions. Women who spend more moneyon drugs could also be having more than one sex act per client in order to earn a higher sexwork income (e.g., regular compared to one-time clients). This could potentially increasetheir vulnerability to HIV/STIs, given that women use condoms less frequently with regularcompared to occasional clients (Hanck et al., 2008, Malta et al., 2008, Reza-Paul et al., 2008and Shannon et al., 2008a).The cost to FSWs associated with street heroin injection was also significantly andindependently related to increased sex work income. In part, this is likely due to theincreased cost for heroin relative to other drugs. Women in sex work who use heroin may bemore economically vulnerable and dependent on sex work for income than women who useother types of drugs, since the average per-point (per-unit) cost of heroin has been shown inour setting to be approximately double the cost of cocaine (Wood et al., 2003). Heroin usershave also been shown to need to use more street heroin due to its low purity compared withprescription heroin. However, since this association remained significant even afteradjusting for the amount of money spent on drugs, women’s dependency on heroinDeering et al. Page 6Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscriptcombined with its higher cost may influence women to engage in higher-risk behaviour forwhich they can earn more money, as described above. In contrast to the relationship withstreet heroin, street-based FSWs who were intensive crack users or cocaine users were notmore likely to earn a higher sex work income. This supports previous research indicatingthat the shift in Vancouver to widely available stimulant crack cocaine, a less expensivestreet drug than injection heroin, may downwardly influence the amount that women cancharge and clients will pay for services (Shannon et al., 2008a). These results also suggestthat the relationship between crack cocaine use and sex work income in a street-based sexmarket may not be adequately captured in a linear model, likely due to several factors,including crack’s low street price, and direct sex-for-crack exchanges (Maher, 2000).Collectively, our findings support global calls, including from the World HealthOrganization, for an evidence-based public health approach to drug use and sex work, and toscale up the availability of treatment, prevention and support (Lutnick and Cohan, 2009,Shannon, 2010 and Wood et al., 2010). Our results in particular underscore the social costsof heroin dependency and indicate that alternative approaches, such as opiate-substitutiontherapy as an essential medicine, should be considered. Recent clinical trials in this settingsuggest that opiate-substitution therapies (including prescription heroin substitution,methadone maintenance therapy, and injectable diacetylmorphine) can be highly effectiveand have been associated with a substantial reduction in average amount of money spent ondrugs (Oviedo-Joekes et al., 2009 and Schwartz et al., 2006), indicating that this could be apotentially important intervention to reduce harm to vulnerable women who engage in sexwork to sustain heroin use. Alternative regulatory practices with respect to drug use thatadhere to evidence-based drug policies would facilitate the scale-up and implementation ofthese new approaches (Wood et al., 2010). Given the clear association between the streetcost of drugs and sex work income in our study, and the relationship between regulatorypractices toward drug use that remove large quantities of drugs from drug markets andsubsequently drive down drug purity while driving up costs (Beyrer et al., 2010, Strathdee etal., 2010 and Wood et al., 2010), such alternative regulatory practices could help reduce sexwork-related harms relating to the increased need to earn higher sex work income to supportdrug use. Improving access and utilization of addictions treatment for women in sex workcould also reduce women’s dependence on sex work earnings to support drug use. Thisapproach should be coupled with other low-threshold training, employment and/or improvedeconomic security (Young and Mulvale, 2009), including evaluation of programs to supporttransitioning out of sex work for survival. Increased economic control for sex workers maybe a critical HIV intervention strategy in promoting condom negotiation with clients, orreducing the likelihood that women will engage in other riskier behaviour in exchange forhigher earnings per sex act. A shift away from current criminalized approaches toprostitution could additionally disentangle the underground sex work and drug markets bymoving sex work to safer indoor work spaces and promoting increased economic controland choice for FSWs (such as FSWs ability to regulate fee structures, opportunities for thosewho wish to exit sex work) (Shannon et al., 2008c). Evidence suggests removal of criminalsanctions would promote sex work occupational safety by reducing violence, increasingaccess to health and social support services and increasing women’s safety and ability tonegotiate condom use with clients (Lutnick and Cohan, 2009, Makin, 2010 and Shannon,2010).When viewed in tandem with studies of income among non-drug using sex workers, ourresults also confirm that youth can generate a higher income from sex work compared witholder sex workers (Gertler et al., 2005 and Moffatt and Peters, 2004). This age differential insex work income may reflect increased bargaining power (and amount charged pertransaction) due to higher demand for young sex workers among male clients, and iscomparable to findings among other entertainment industries and levels of the sex workDeering et al. Page 7Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscriptindustry (Shannon et al., 2008a). While younger women in our study were also more likelyto spend more on drugs, the association between younger age and higher sex work incomewas retained after adjusting for drug use patterns as well as the numbers of clients.This study has several limitations. The study population included only women in street-levelsex work; since sex work is conducted across many other types of venues (e.g., massageparlours, brothels), the results may not be generalizable to FSWs in other venues. Sincesampling frames are difficult to construct for hidden populations including FSWs, thesample was not randomly generated and may not be representative of street-based FSWs inother settings. However, to address these challenges, time-space sampling was used tosystematically sample women at staggered times and locations based on street-levelsolicitation spaces identified through mapping, therefore helping attract a representativesample (Stueve et al., 2001). Some questions may also be perceived to be sensitive,including sex work income, and thus self-reported behaviour may be subject to socialdesirability bias or higher non-response rates. To address this, women were interviewed in aplace where they felt comfortable (including the local sex work service agency or the studysite). Women were interviewed by their peers (current or former sex workers), helping toincrease their comfort and accuracy of responses. The study measures also were developedthrough extensive input from the community of sex workers, service providers and otherstakeholders. We also found no significant differences between samples of women who didand did not provide valid responses to the survey item on sex work income. We targeted adifficult-to-access, hidden and marginalized population with high health care and drugtreatment needs; the use of regression with GEEs allowed us to adjust for multiplemeasurements made on the same participant at different follow-ups. Although it is notpossible to confirm the direction of association, the relationship between sex work incomeand money spent on drugs is significant, even when we adjusted for other factors includingthe numbers of clients and the amount of money earned through other sources, and issupported by ethnographic research indicating the strong relationship between level ofaddiction and involvement in sex work (Maher, 2000, Shannon et al., 2007, Shannon et al.,2008a and Strathdee et al., 2008).In summary, our study findings indicate a crucial need to scale up access and availability ofevidence-based harm reduction and addiction treatment strategies, including heroinmaintenance therapy and alternative regulatory frameworks for drug use. Our results suggestthe need to rigorously pilot and evaluate evidence-based interventions that promoteeconomic control and choice among street-based sex workers, alongside removal of criminalsanctions targeting sex work.AcknowledgmentsWe thank the women for time and expertise and our peer research team (Shari, Laurie, Chanel, Rose, Shawn,Tammy, Adrian). We thank our community advisory board and sex work and community partner agencies, as wellas Peter Vann, Ruth Zhang, Calvin Lai and Kate Gibson for their research and administrative support.Role of funding source: This research was primarily funded through an operating grant from the Canadian Institutesof Health Research (CIHR) and National Institutes of Health Research (grant #1R01DA028648-01A1). KND issupported by the CIHR. JS is supported by an Applied Public Health Chair from the CIHR. MWT is supported bythe Michael Smith Foundation for Health Research. KS is partially supported by a CIHR New Investigator Awardand NIH (grant #1R01DA028648-01A1). The funders had no role in study design, data collection, or in analysisand interpretation of the results, and this paper does not necessarily reflect views or opinions of the funders.Deering et al. Page 8Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptREFERENCESFAQ. How do I interpret a regression model when some variables are log transformed?. AcademicTechnology Services, Statistical Consulting Group; UCLA: 2010.n.d., accessed onAral SO, St. Lawrence JS. The Ecology of Sex Work and Drug Use in Saratov Oblast, Russia.Sexually Transmitted Diseases. 2002; 29:798–805. [PubMed: 12466723]Beyrer C, Malinowska-Sempruch K, Kamarulzaman A, Kazatchkine M, Sidibe M, Strathdee SA. Timeto act: a call for comprehensive responses to HIV in people who use drugs. 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Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptDeering et al. Page 13Table 1Select factors describing the sample of female sex workers in Vancouver, Canada, with valid responses to theoutcome ‘average sex work income earned per week’ at their first survey administered. Median sex workincome (interquartile range) is also provided, across social and environmental factors and sex work and druguse patterns.Factors Percent(N) N = 129Median sex workincomeMedian amount earned from sex work per weekb $300 ($100–$560)Median amount spent on drugs per weekb $400 ($150–$780)Median amount earned per week through otherincomea,b $700 ($525–$1000)Median numbers of clients per weekb 5.5 (2–13)Age<25 years 39.5 (51) $500 ($200–$800)25+ years 60.5 (78) $200 ($100–$500)EthnicityCaucasian 46.5 (60) $435 ($145–$600)Ethnic minority 53.5 (69) $200 ($100–$500)Currently homelessYes 40.3 (52) $200 ($100–$650)No 59.7 (77) $300 ($140–$500)Inject heroinbYes 44.2 (57) $500 ($200–$800)No 55.8 (72) $200 ($100–$500)Inject cocainebYes 32.6 (42) $300 ($100–$600)No 67.4 (87) $250 ($100–$500)Inject/smoke crystal methbYes 18.6 (24) $290 ($100–$800)No 81.4 (105) $300 ($150–$500)Daily intensive crack smokingbYes 35.7 (46) $500 ($200–$600)No 64.3 (83) $200 ($100–$560)Receptive sharing of used pipe and/or syringebYes 51.9 (67) $225 ($150–$700)No 48.1 (62) $300 ($100–$500)Had an intimate partnerbYes 45.8 (54) $300 ($150–$500)No 54.2 (64) $300 ($100–$750)Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptDeering et al. Page 14Factors Percent(N) N = 129Median sex workincomePressured into unprotected sex by clientbYes 29.4 (32) $300 ($175–$580)No 70.6 (77) $300 ($200–$600)Condoms always used by clientbYes 17.1 (21) $350 ($200–$800)No 82.9 (102) $275 ($100–$560)Exchange sex while on crackbYes 59.1 (65) $300 ($150–$500)No 40.9 (45) $200 ($100–$500)Solicit in main/commercial areasbYes 32.6 (42) $500 ($200–$800)No 67.4 (87) $200 ($100–$500)Solicit in alleys/industrial areasbYes 31.0 (40) $300 ($100–$500)No 69.0 (89) $300 ($150–$600)Service clients mainly in indoor public placesbYes 51.2 (66) $212 ($100–$560)No 48.8 (63) $350 ($150–$600)Service clients mainly in outdoor public placesbYes 33.3 (43) $420 ($200–$600)No 67.7 (86) $200 ($100–$560)aIncludes government-administered income (welfare, disability, nutritional supplement), legal informal sources (binning, panhandling, partner’sincome, under-the-table job), legal formal sources (temporary job, regular job) as well as non-legal sources (drug-related, i.e. dealing).bLast six months.Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptDeering et al. Page 15Table 2Multivariable GEE coefficients for linear regression of the relationship between social, drug use andenvironmental factors and sex work income (log), and 95% confidence intervals (CIs) for coefficients.Factor Coefficient (95% CIs) p-ValueAmount spent on drugs per week (log) 0.20 (0.04–0.36) 0.017Amount earned from other income per weeka NS –Numbers of clients per week (log) 0.32 (0.19–0.42) <0.001Age <25 years 0.36 (0.08–0.64) 0.012Caucasian NS –Currently homeless NS –Inject heroinb 0.41 (0.11–0.70) 0.007Inject cocaineb NS –Inject/smoke crystal methb NS –Daily intensive crack smokingb 0.02 (−0.31 to 0.35) 0.888Receptive sharing of used pipe and/or syringeb NS –Had an intimate partnerb NS –Pressured into unprotected sex by clientb NS –Condoms always used by client 0.31 (−0.01 to 0.65) 0.065Exchange sex while on crackb,cSolicit in main/commercial areasb NS –Solicit in alleys/industrial areasb NS –Service clients indoorsb NS –Service clients outdoorsb NS –aIncludes government-administered income (welfare, disability, nutritional supplement), legal informal sources (binning, panhandling, partner’sincome, under-the-table job), legal formal sources (temporary job, regular job) as well as non-legal sources (drug-related, i.e. dealing).bLast six months.cSample size of valid responses too small to include in multivariable analysis.Drug Alcohol Depend. Author manuscript; available in PMC 2012 November 01.


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