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High Prevalence and Partner Correlates of Physical and Sexual Violence by Intimate Partners among Street… Argento, Elena; Muldoon, Katherine Anne; Duff, Putu; Simo, Annick; Deering, Kathleen N.; Shannon, Kate Jul 10, 2014

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High Prevalence and Partner Correlates of Physical andSexual Violence by Intimate Partners among Street andOff-Street Sex WorkersElena Argento1, Katherine A. Muldoon2, Putu Duff1,2, Annick Simo1, Kathleen N. Deering1,3,Kate Shannon1,2,3*1Gender and Sexual Health Initiative, British Columbia Centre for Excellence in HIV/AIDS, Vancouver, British Columbia, Canada, 2 School of Population and Public Health,University of British Columbia, Vancouver, British Columbia, Canada, 3Department of Medicine, University of British Columbia, Vancouver, British Columbia, CanadaAbstractObjectives: Intimate partner violence (IPV) is associated with increased risk of HIV among women globally. There is limitedevidence and understanding about IPV and potential HIV risk pathways among sex workers (SWs). This study aims tolongitudinally evaluate prevalence and correlates of IPV among street and off-street SWs over two-years follow-up.Methods: Longitudinal data were drawn from an open prospective cohort, AESHA (An Evaluation of Sex Workers HealthAccess) in Metro Vancouver, Canada (2010–2012). Prevalence of physical and sexual IPV was measured using the WHOstandardized IPV scale (version 9.9). Bivariate and multivariable logistic regression using Generalized Estimating Equations(GEE) were used to examine interpersonal and structural correlates of IPV over two years.Results: At baseline, 387 SWs had a male, intimate sexual partner and were eligible for this analysis. One-fifth (n = 83, 21.5%)experienced recent physical/sexual IPV at baseline and 26.2% over two-years follow-up. In multivariable GEE analysis, factorsindependently correlated with physical/sexual IPV in the last six months include: childhood (,18 years) sexual/physicalabuse (adjusted odds ratio [AOR] = 2.05, 95% confidence interval [CI]: 1.14–3.69), inconsistent condom use for vaginal and/oranal sex with intimate partner (AOR= 1.84, 95% CI: 1.07–3.16), ,daily prescription opioid use (AOR= 1.72, 95% CI: 1.02–2.89), providing financial support to intimate partner (AOR= 1.65, 95% CI: 1.05–2.59), and sourcing drugs from intimatepartner (AOR= 1.62, 95% CI: 1.02–2.26).Discussion: Our results demonstrate that over one-fifth of SWs in Vancouver report physical/sexual IPV in the last sixmonths. The socio-structural correlates of IPV uncovered here highlight potential HIV risk pathways through SWs’ intimate,non-commercial partner relationships. The high prevalence of IPV among SWs is a critical public health concern andunderscores the need for integrated violence and HIV prevention and intervention strategies tailored to this key population.Citation: Argento E, Muldoon KA, Duff P, Simo A, Deering KN, et al. (2014) High Prevalence and Partner Correlates of Physical and Sexual Violence by IntimatePartners among Street and Off-Street Sex Workers. PLoS ONE 9(7): e102129. doi:10.1371/journal.pone.0102129Editor: Joseph R. Zunt, University of Washington, United States of AmericaReceived November 21, 2013; Accepted June 16, 2014; Published July 10, 2014Copyright:  2014 Argento et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permitsunrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Funding: This research was supported by operating grants from the United States National Institutes of Health (R01DA028648) and Canadian Institutes of HealthResearch (HHP-98835). KS is supported by U.S. National Institutes of Health (R01DA028648), Canadian Institutes of Health Research and Michael Smith Foundationfor Health Research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Competing Interests: The authors have declared that no competing interests exist.* Email: gshi@cfenet.ubc.caIntroductionMale-perpetrated intimate partner violence (IPV) is a pervasivehuman rights violation and public health concern, with substantialnegative impacts on morbidity and mortality, including poorsexual and reproductive health outcomes, HIV, and sexuallytransmitted infections (STIs) [1,2]. It is estimated that up to 60%of women globally will experience physical and/or sexual violencein their lifetime, most commonly from their intimate partners:30% of women worldwide who have ever been in a relationshiphave experienced physical and/or sexual IPV [3,4]. IPV includesviolence in the form of ‘‘sexually, psychologically and physicallycoercive acts used against adult and adolescent women by acurrent or former intimate partner, without her consent’’ [4].Immediate consequences of IPV include injuries and death fromphysical assault, unintended pregnancies, HIV/STIs, and psycho-logical distress [5]. Long-term conditions associated with IPVinclude chronic pain conditions, gastro-intestinal syndromes andother physical disabilities [6], post-traumatic stress disorder,depression, anxiety, substance abuse, and suicide [7,8]. Thereare likely multifactorial pathways through which IPV increases riskfor these adverse health outcomes and the direct effects of physicaltrauma and the long-term accumulation of stress may be keycontributing factors [9]. The UN has declared an urgent need tostrengthen the knowledge base on all forms of violence againstwomen to inform policy and strategy development [10].In North America, male-perpetrated IPV is associated with asignificant burden. In the U.S., the 2010 National IntimatePartner and Sexual Violence Survey indicated that 30% of womenPLOS ONE | www.plosone.org 1 July 2014 | Volume 9 | Issue 7 | e102129experience physical IPV and 17% sexual IPV in their lifetimes[11]. In a 2003 review and critique of 16 Canadian prevalencestudies, the annual prevalence of physical abuse among Canadianwomen ranged from 0.4% to 18%, and lifetime prevalence ofphysical or sexual abuse by their male partners ranged from 8.0%to 36.4% [12]. Another Canadian study that examined data fromthe 1999 Canadian General Social Survey for gender patterns ofIPV found that being younger, divorced/separated or single,having children in the household, and poor self-rated health weresignificant risk factors for physical/sexual IPV [13]. The 2005report on the WHO Multi-Country Study on Women’s Healthand Domestic Violence Against Women estimated the lifetimeprevalence of physical or sexual IPV among ever-partneredwomen to range from 15% to 71%, with past year prevalenceestimated between 4% and 54% [14].Other studies from around the world have documented theassociation between partner violence and gender inequality withincreased risk of HIV [1,15–17]. A 2010 longitudinal study of1099 women (aged 15–26) from South Africa demonstrated strongtemporal evidence between IPV and incident HIV infection:approximately one in seven incident HIV infections among theyoung women were attributable to either IPV or low gender equityin their relationships [18]. A 2013 longitudinal study in Ugandaalso found an association between lifetime IPV and risk of incidentHIV infection, which tended to be greater for women who wereexposed to more severe and frequent IPV and for a longerduration [19].Despite growing data on the magnitude and correlates of IPVamong the general population of women of reproductive ageglobally [20–22], there is a surprising dearth of research on IPVexperiences among marginalized and stigmatized populations,such as sex workers (SWs), women who use drugs, homelesswomen and female youth, particularly in high income settings.Globally, SWs continue to face a disproportionate amount ofviolence [23–25]. While IPV among women who use drugs hasreceived some attention [26–28], there are very few epidemiolog-ical studies on IPV among SW populations, and the majority ofresearch has been done in lower-middle income countries (LMIC)such as India, Mexico, Kenya, and other Sub-Saharan African(SSA) settings [29–31]. Based on a recent global systematic review,past year physical/sexual IPV prevalence rates among SWs wereestimated to range from 8% to 61%, while lifetime prevalence ofany type of IPV (physical, sexual or emotional) ranged from 4% to73% [25]. A longitudinal study in the U.S. of 416 women enrolledin methadone maintenance treatment programs found significantbi-directional temporal relationships between sexual and/orphysical IPV and risk of sexual HIV/STI transmission (i.e.inconsistent/no condom use and IPV and inconsistent/no requestsfor partners to use condoms and IPV) [26].Qualitative and ethnographic research among marginalizedgroups of women (street-involved SWs and young, homeless drugusers) has documented the pervasiveness of controlling and abusiveboyfriends, providing some contextual understanding around thepower imbalances and associated violence that directly influenceswomen’s agency and ability to safeguard against risky sexual anddrug-using behaviors, making these populations particularlyvulnerable to transmission of HIV/STIs [27,28,32]. As sexualexclusivity is highly valued in intimate relationships in Westernsocieties, SWs and their intimate partners may struggle withnotions of infidelity and trust within the context of sex work [33].Other qualitative studies have suggested that intimate partners ofSW may be jealous of clients [34], facilitating pathways toviolence.There is a critical need for research on IPV among marginal-ized groups, including SWs. The objectives of this study weretherefore to examine the prevalence of physical and sexual IPVagainst a cohort of SWs in Vancouver, Canada and to describe thesocio-structural correlates of IPV.MethodsStudy Design and SampleData for this study were drawn from AESHA (An Evaluation ofSex Workers Health Access), an open prospective cohort of femaleSWs (2010–2012) who conduct sex work in both street (public) andoff-street (indoor) settings. Eligibility criteria for AESHA partici-pants at baseline includes being female (including transgender,male-to-female), older than 14 years of age, having exchanged sexfor money within the last 30 days, and providing written informedconsent. This analysis is restricted to AESHA participants whoreported having at least one intimate partner, which is defined ashaving a sexual, non-commercial, male partner in the last sixmonths, at baseline.In the context of hard-to-reach populations, SWs were recruitedthrough time-location sampling and community mapping strate-gies. Day and late night peer-outreach was used to identify bothoutdoor sex work locations (i.e. streets, alleys) and indoor sex workvenues (i.e. massage parlors, micro-brothels, and in-call locations)across Metro Vancouver. In addition, online recruitment was usedto reach SWs working through online solicitations spaces.At enrolment and on a bi-annual basis, participants complete aninterview-administered questionnaire by a trained interviewer andHIV/STI/HCV (hepatitis C virus) serology testing by a projectnurse. The main interview questionnaire elicits responses relatedto socio-demographics (e.g. sexual identity, ethnicity, housing), sexindustry work (e.g. work environment, solicitation, social cohesionand support, access to services, violence and safety, incarceration),clients (e.g. number/type of clients, types of services, condom use),intimate partners (e.g. sexual history, cohabitation, financialsupport), trauma and violence (e.g. lifetime and childhood trauma,exposure to intimate partner and occupational violence), and druguse patterns (injection and non-injection). In addition, a clinicalquestionnaire is administered relating to overall physical, mentaland emotional health, sexual and reproductive health, and HIVtesting and treatment experiences. SWs have the option to visitone of two study offices or complete the questionnaire and nursingcomponent at a safe location identified by them, including work orhome locations. All participants receive an honorarium of$40CAD at each bi-annual visit for their time, expertise and travel.Ethics StatementThe AESHA study holds ethical approval through ProvidenceHealth Care/University of British Columbia Research EthicsBoard and has a community advisory board of over 15 agencies.Study VariablesIPV Outcome. Recent IPV was measured using an abridgedversion of the WHO Standardized IPV Scale Version 9.9 [14,35].The scale was originally developed for the WHO Multi-countryStudy on Women’s Health and Domestic Violence AgainstWomen in response to large discrepancies in research designand methods, making comparison of data between settingsdifficult. The standardized scale elicits responses from womenabout experiences of physically and sexually violent acts by acurrent or former intimate male partner, and about selectedsymptoms associated with physical and mental health. The threeviolence components (physical, sexual and emotional) are eachIntimate Partner Violence among Sex WorkersPLOS ONE | www.plosone.org 2 July 2014 | Volume 9 | Issue 7 | e102129validated separately and as a single scale [14,35,36]. For thepurposes of this analysis, and due to substantial overlap betweensexual and physical IPV, our outcome measure was moderate orsevere physical and/or sexual violence by any male intimate (non-commercial) partner in the last six months and was time-updatedat each follow-up visit. The emotional violence component of theWHO scale was not included in this analysis. Physical violenceincluded both ‘‘moderate’’ (‘‘yes’’ response to one or more of:slapped or thrown something; pushed or shoved) and/or ‘‘severe’’(‘‘yes’’ response to one or more of: hit with a fist; kicked, draggedor beaten up; choked or burnt; threatened to use or used a gun orother weapon), while sexual IPV included ‘‘yes’’ responses to oneor more of the following: forced to have sex against will, having sexout of fear, and forced to perform degrading or humiliating sexualacts.Individual and Socio-Demographic Variables. Studyvariables for potential correlates of IPV were selected based onthe literature and available data collected for the AESHA cohortbetween 2010 and 2012. Fixed variables considered at baselineincluded demographic variables such as: age (continuous), sexualminority (lesbian, gay, bisexual, transgender, transsexual, or two-spirited), being of Aboriginal/Indigenous ancestry (inclusive ofFirst Nations, Metis, and Inuit), and being a migrant/newimmigrant worker (versus Canadian born). Historical exposureto childhood physical and/or sexual abuse (,18 years of age) wasalso included. Individual variables including frequency of use ofinjection and non-injection illicit drugs (daily, less than daily or nouse) were time-updated, and based on the last six months at eachfollow-up.Partner-Level Data. The study participants provided allinformation relating to their partners, as the partners themselveswere not interviewed. Partner-level data were time-updated, co-variates were collected at baseline and each follow-up visit for theprimary intimate sex partner, and included inconsistent condomuse for vaginal/anal sex with intimate partners, condom refusal byintimate partner, cohabitating with intimate partner, sourcingdrugs (not including pot or alcohol) from intimate partner, andfinancial support provided to or by an intimate partner. Whetheror not intimate partners had other sexual partners (bothcommercial and non-commercial) was also included.Statistical AnalysesAnalyses were restricted to AESHA participants who reportedhaving at least one recent intimate (non-commercial) male sexpartner (last six months). Socio-demographic variables (age,ethnicity, sexual minority, migrant status) were considered fixedvariables. All other variables were considered time varying, andwere updated to reflect their occurrence within the last six months.All time-updated variables were measured at the same time periodas the outcome. Correlates of IPV were examined using bivariateand multivariable logistic regression using Generalized EstimatingEquations (GEE), with a logit link for dichotomous variables. Toadjust the standard error and account for correlations arising fromthe four repeated measurements on the same participant over thetwo-years follow-up period, an exchangeable correlation matrixwas used. GEE accounts for missing data using the GEEestimating equation, that substitutes data from non-missing pairsinto the estimators of the correlations matrix. Variables signifi-cantly associated with IPV at the p,0.05 level in bivariatescreening were subsequently fitted into a multivariable GEE modelto adjust for potential confounding. The multivariable model wasconstructed using Quasi-likelihood Information Criteria (QIC)selection, which has been used successfully in past research by ourgroup [37]. The backward model selection procedure (QIC)identifies the model with the best overall fit as indicated by thelowest quasi-likelihood under the independence model criterionvalue [38]. Two-sided p-values and unadjusted and adjusted oddsratios (OR and AOR) with 95% confidence intervals (95%CI) arereported. All statistical analyses were performed using SASsoftware package version 9.3 (SAS Institute, Cary, NC, USA).ResultsSocio-Demographic CharacteristicsOf the total cohort (n = 652), our analyses were restricted toparticipants who reported having at least one male, intimatesexual partner in the past six months for a sample of 387 street andoff-street SWs. At baseline, one-fifth (n = 83, 21.5%) of womenreported experiencing moderate or severe physical and/or sexualIPV in the last six months. The median age of all participants was34 (interquartile range [IQR]= 28–41, minimum age= 17,maximum age= 58), with those who reported recent IPV beingslightly younger than those who did not: 32 (IQR: 25–39) vs. 35(IQR: 28–42) (p = 0.003). Most women (76.2%) were Canadian-born, and 39.0% self-identified as being of Aboriginal ancestry.Almost one quarter (24.3%) of participants reported being a sexualminority. The majority (66.7%) of SWs reported physical and/orsexual abuse before age 18 and this was higher among those whohad experienced recent IPV compared to those who had not(84.3% vs. 61.8%) (p,0.001). Baseline socio-demographic andpartner-level characteristics of participants who experienced IPVin the last six months compared to those who did not are displayedin Table 1.Regarding drug use, 72.1% of SWs at baseline had used non-injection illicit drugs and 40.8% had injected drugs in the last sixmonths. At baseline, the number of SWs who reported usingprescription opioids (POs) less than daily was 63 (16.3%), whichwas higher among those with IPV (28.9%) than those without(12.8%) (p= 0.003). Non-injection and injection drug use byintimate partners was reported at 63.6% and 21.2%, respectively,and 37.5% of participants reported sourcing drugs from theirintimate partners. In the last six months, 39.0% of SWs were livingwith their intimate partners and 13.7% of intimate partners hadother sex partners.Bivariate & Multivariable GEE AnalysesBivariate and multivariable odds ratios for correlates with recentIPV are displayed in Table 2. In the bivariate GEE analysis,factors found to be significantly positively correlated with recentphysical/sexual IPV at a p,0.05 level included condom refusal forvaginal and/or anal sex by an intimate partner (Odds Ratio [OR]4.48, 95% Confidence Interval [95%CI] 1.63–12.28), beingCanadian-born (OR 3.36, 95%CI 1.69–6.69), childhood physicaland/or sexual abuse ,18 years (OR 3.34, 95%CI 1.89–5.90),non-injection drug use (OR 3.12, 95%CI 1.72–5.62), sourcingdrugs from an intimate partner (OR 2.77, 95%CI 1.85–4.14), non-injection drug use by intimate partner (OR 2.61, 95%CI 1.63–4.18), injection drug use by intimate partner (OR 2.56, 95%CI1.66–3.94), providing financial support to an intimate partner (OR2.40, 95%CI 1.60–3.59), less than daily PO use (OR 2.38, 95%CI1.46–3.88), inconsistent condom use in vaginal and/or anal sexwith an intimate partner (OR 2.27, 95%CI 1.39–3.71), intimatepartner had other non-SW sex partners (OR 2.03, 95%CI 1.08–3.80), and injection drug use (OR 1.66, 95%CI 1.12–2.47).In the multivariable GEE analysis, factors independentlycorrelated with recent physical/sexual IPV over the last sixmonths include: childhood physical and/or sexual abuse ,18years (Adjusted Odds Ratio [AOR] 2.05, 95%CI 1.14–3.69),Intimate Partner Violence among Sex WorkersPLOS ONE | www.plosone.org 3 July 2014 | Volume 9 | Issue 7 | e102129inconsistent condom use for vaginal and/or anal sex with intimatepartner (AOR 1.84, 95%CI: 1.07–3.16), less than daily PO use(AOR 1.72, 95%CI 1.02–2.89), providing financial support tointimate partner (AOR 1.65, 95%CI 1.05–2.59), sourcing drugsfrom intimate partner (AOR 1.62, 95%CI 1.02–2.26) and youngerage (AOR 0.96 per increasing year of age, 95%CI 0.93–0.98).DiscussionOur longitudinal study demonstrates that over one-fifth of SWsin Metro Vancouver report moderate or severe physical and/orsexual IPV in the last six months. Experiencing recent IPV wasindependently associated with early childhood exposure tophysical and/or sexual abuse, while partner-level factors emergedas key correlates over the course of follow-up, includinginconsistent condom use, economic dependence of male intimatepartner on sex worker, and sourcing drugs from an intimatepartner.The high prevalence of recent IPV among street and off-streetSWs in our study is a critical and neglected human rights andpublic health concern and underscores the pressing need to focuson marginalized and hidden populations. Our results supportexisting literature documenting elevated levels of violence faced bySWs in Vancouver [32,39–41] and highlight important socio-structural factors that intersect with violence within SWs’ intimate,non-commercial partner relationships. While growing research hasexamined workplace violence (e.g., by clients, police, communitymembers) against SWs [42–44], there are very few population-based studies that investigate the factors influencing violencewithin SWs’ intimate partner relationships. This is despiteobservations that SWs experience structural and individual factorsthat heighten their risk for IPV, including high rates ofhomelessness [45] high rates of childhood maltreatment [46,47],and high rates of unplanned pregnancy [48,49].The overlap between gender inequality and heightened risk ofHIV plays an important role in the context of IPV against SWs. Itis estimated that SWs have more than 13-times increased odds ofhaving HIV compared to the general female population [50], andphysical and/or sexual IPV has been found to be significantlyassociated with both higher levels of HIV risk behaviors andincident HIV infection among women globally [1,16,18].Research demonstrates that experiences of IPV are often anextension of unequal gender roles and power imbalances inrelationships; higher gender inequity has been found to beindependently associated with increased male-controlled sexualdecision making power, perpetration of rape, unprotected sex andmultiple/concurrent sex partners [15].Among drug-using women in particular, power dynamics withtheir intimate partners often favour traditional gender roles wheremen exert significant control over the relationship, includingnegotiating sexual risk-reduction behaviours. Bi-directional tem-Table 1. Socio-demographic and partner-level characteristics of sex workers (SWs) in Metro Vancouver who experienced physicaland/or sexual intimate partner violence (IPV) compared to those who did not, at baseline.Characteristics Total N=387 IPV n=83 No IPV n=304 p-valueSociodemographic Variables (n,%)Age (med, IQR) 34 (28–41) 32 (25–39) 35 (28–42) 0.003Canadian-born 295 (76.2) 73 (88.0) 222 (73.0) 0.003Aboriginal ancestry 151 (39.0) 35 (42.2) 116 (38.2) 0.508Physically or sexually abused before age 18 258 (66.7) 70 (84.3) 188 (61.8) ,0.001HIV seropositivity 38 (9.8) 4 (4.8) 34 (11.1) 0.063STI seropositivity 38 (9.8) 6 (7.2) 32 (10.5) 0.355Sexual minority 94 (24.3) 20 (24.1) 74 (24.3) 0.963Coerced into sex work 47 (12.1) 11 (13.3) 36 (11.8) 0.730Daily prescription opioid use{ 11 (2.8) 1 (1.2) 10 (3.3) 0.003Less than daily prescription opioid use{ 63 (16.3) 24 (28.9) 39 (12.8) 0.003Injection drug use{ 158 (40.8) 39 (47.0) 119 (39.1) 0.200Non-injection drug use{ 279 (72.1) 73 (88.0) 206 (67.8) ,0.001Partner-Level Variables (n,%)Intimate Partner (IP) used injection drugs{ 82 (21.2) 30 (36.1) 52 (17.1) ,0.001IP used non-injection drugs{ 246 (63.6) 67 (80.7) 179 (58.9) ,0.001Inconsistent condom use in vaginal/anal sex with IP{ 273 (70.5) 66 (79.5) 207 (68.1) 0.038Condom refusal by IP{ 10 (2.5) 5 (6.0) 5 (1.6) 0.033Scored drugs from intimate partner{ 145 (37.5) 49 (59.0) 96 (31.6) ,0.001Financial support provided to IP{ 122 (31.5) 39 (47.0) 83 (27.3) ,0.001Financial support provided by IP{ 241 (62.3) 46 (55.4) 195 (64.1) 0.149IP has other SW sex partners{ 48 (12.4) 12 (14.5) 36 (11.8) 0.528IP has other non-SW sex partners{ 53 (13.7) 16 (19.3) 37 (12.17) 0.107Cohabitating with IP{ 151 (39.0) 33 (39.8) 118 (38.8) 0.876{In the last 6 months.Note: Study participants provided all partner-level data.doi:10.1371/journal.pone.0102129.t001Intimate Partner Violence among Sex WorkersPLOS ONE | www.plosone.org 4 July 2014 | Volume 9 | Issue 7 | e102129poral relationships between sexual and physical IPV and risk ofHIV/STI transmission have been demonstrated among drug-using women in the U.S, where inconsistent/no condom use andrequesting partners to use condoms was significantly associatedwith IPV [26].Qualitative research among substance-using women in survivalsex work underscores the role of structural violence and genderedpower inequities in shaping HIV and the need to facilitateenabling environments [32]. The normalization of physical, sexualand emotional violence among drug-using women in streetenvironments makes these populations particularly vulnerable,especially where economic dependence and drug sharing occurswithin sexual partnerships [28,32]. Furthermore, in the context ofincreasing misuse of POs and associated harms in North America,and in light of our study’s results correlating IPV with the use ofPOs, there is a need to further investigate the mechanism linkingPOs and IPV among SWs. Evidence suggests that the misuse ofPOs now constitutes the third highest level of substance use burdenof disease in Canada, after alcohol and tobacco [51].This study’s findings that childhood abuse is positivelyassociated with recent IPV, often referred to as ‘‘re-victimization’’,is consistently documented in many settings [7], includingpsychiatric populations [52], the general population [53,54], andvulnerable populations such as injection drug users [55].Experiences of violence in childhood tend to ‘‘normalize’’ theabuse, increasing the likelihood of re-victimization and perpetu-ating the cycle of violence. Meta-analyses have concluded thatbetween 15%–79% of women with histories of childhood traumaexperience sexual violence as adults [56]. Within this study, analarming 67% of the sample reported experiencing physical orsexual abuse before the age of 18, reinforcing a cycle of violencethat contributed to 3.34 times the odds of experiencing recent IPV(95% CI: 1.89–5.90). A comparable study of 300 female SWs intwo Mexico-U.S. border cities found that those who experiencedabuse as a child were also more likely (OR=2.49, 95% CI: 1.52–4.10) to have experienced recent IPV [30]. Antecedent studieshave also shown that among a cohort of street involved youth inVancouver, moderate to severe childhood trauma scores wereassociated with entry into sex work [47]. These findingssubstantiate the need for structural interventions that increasechild protections and prevent future violence and risk.Although violence between partners occurs at the interpersonal-level, the larger macro-level context plays an important role insustaining cultures of complacency that tolerate gender-basedviolence, including against SWs. The criminalized nature of thesex industry in Canada drives a culture of stigma among SWs thatleads to a cycle of violence that is ultimately fuelled by powerinequity. Laws that further marginalize SWs not only constraintheir choices occupationally, but also undermine their health ingeneral: stigma associated with sex work prevents SWs fromaccessing health care services needed for violence treatment andprevention [57].Implementing screening instruments for IPV in reproductive/primary health care and low-threshold support settings formarginalized populations, may help to more accurately detectIPV and direct focus toward SWs’ often overlooked non-commercial relationships. However, there continues to be debatearound the extent to which screening effectively improves healthoutcomes for women [58,59]. New WHO practice and policyguidelines now discourage universal screening in the generalpopulation, based on a lack of evidence demonstrating thatscreening for IPV produces better outcomes for women [60,61].Among marginalized populations, the challenges with effectiveIPV screening remain related to implementation, follow-up andsupport, with new research suggesting value in a systems approachto IPV screening among key populations [62]. Stigma remains aprimary barrier to accessing violence prevention and health careservices for SWs. Thus, health care facilities and programs mustTable 2. Longitudinal bivariate and multivariate GEE of correlates of physical and/or sexual intimate partner violence (IPV) amongstreet and off-street sex workers (SWs) with a male, intimate partner (IP) in the AESHA Cohort (n = 387).Unadjusted AdjustedCharacteristic Odds Ratio (95% CI) Odds Ratio (95% CI)Younger Age 0.95 (0.93–0.98)** 0.96 (0.93–0.98)**Canadian-born (vs. Migrant) 3.36 (1.69–6.69)** -Physically and/or sexually abused before age 18 3.34 (1.89–5.90)** 2.05 (1.14–3.69)*Daily prescription opioid use{ 0.44 (0.07–2.82) 0.35 (0.05–2.62)Less than daily prescription opioid use{ 2.38 (1.46–3.88)** 1.72 (1.02–2.89)*Inconsistent condom use in vaginal/anal sex with IP{ 2.27 (1.39–3.71)** 1.84 (1.07–3.16)*Condom refusal by IP{ 4.48 (1.63–12.28)** -Financial support provided to IP{ 2.40 (1.60–3.59)** 1.65 (1.05–2.59)*Sources drugs from IP{ 2.77 (1.85–4.14)** 1.62 (1.02–2.56)*Non-injection drug use{ 3.12 (1.72–5.62)** 1.96 (0.96–4.00)Injection drug use{ 1.66 (1.12–2.47)* -IP used non-injection drugs{ 2.61 (1.63–4.18)** -IP used injection drugs{ 2.56 (1.66–3.94)** -IP had other non-SW sex partners{ 2.03 (1.08–3.80)* -*p,0.05.**p,0.01.{In the last 6 months.Note: Study participants provided all partner-level data.doi:10.1371/journal.pone.0102129.t002Intimate Partner Violence among Sex WorkersPLOS ONE | www.plosone.org 5 July 2014 | Volume 9 | Issue 7 | e102129adapt to improve access to this highly stigmatized group byproviding sensitivity training and fostering environments free fromdiscrimination at all levels [57], in partnership with sex workcommunities.LimitationsThis study has a number of strengths and limitations that shouldbe considered in the interpretation of our study. The longitudinaldesign and analytic methods (GEE) are considered strengths of thisstudy, increasing the number of observations, and allowing foraverage estimates of the correlates of IPV over a two-year period.However, as our analyses did not allow for temporal associations,we were unable to determine causality between the study variablesand IPV. Many of the variables examined in our study weresensitive (i.e. childhood abuse, drug use) and IPV is a highlystigmatizing topic, which may have resulted in under-reporting orrespondent-driven reporting biases in violence by our participants.However, the WHO Standardized IPV Scale used in this studywas designed to ask a limited number of questions pertaining tocommon acts in violent partnerships rather than requiringrespondents to identify themselves as abused – an approach thathas been shown to encourage greater disclosure of violence [35].The scale uses a relatively conservative definition of IPV and isthus more likely to underestimate rather than overestimate thetrue prevalence of violence. Furthermore, interviews wereconducted in safe and comfortable spaces by experiencedinterviewers. The exclusion of the emotional violence componentof the scale in this study may be seen as a limitation, as it may havebiased the associations found by underestimating IPV as a whole.However, without the development of sound methodology foreliciting and measuring emotional violence experiences in relationto physical and sexual violence, it is difficult to ascertain ifemotional violence should be conceptualized as a risk factor forphysical/sexual IPV or rather a constituent element. Although ourfindings may not be fully generalizable to other SW populationsand settings, our study population included SWs from a wide-ranging representation of sex work environments.ConclusionThe magnitude of physical and/or sexual IPV reported by SWsin our study demonstrates a critical need to focus on marginalizedand stigmatized SW populations. SWs remain entrenched in acycle of violence that often started in childhood and continues toimpact their current intimate relationships. Our findings highlightkey factors associated with IPV, including childhood exposure tophysical or sexual violence, inconsistent condom use with intimatepartners, economic dependence and sourcing drugs from anintimate partner, as well as PO use among SWs. The correlates ofIPV uncovered here highlight important socio-structural factorsthat intersect with violence within SWs’ intimate, non-commercialpartner relationships and underscore the need for furtherprevention and intervention strategies tailored to this keypopulation, who continue to experience a disproportionate burdenof violence.AcknowledgmentsWe thank all those who contributed their time and expertise to this project,including participants, partner agencies and the AESHA CommunityAdvisory Board. We wish to acknowledge Peter Vann, Gina Willis, SabinaDobrer, Ofer Amram, Paul Nguyen, Jill Chettiar, Jennifer Morris, RachelNicoletti, Julia Homer, Emily Leake, Chrissy Taylor, Vivian Lui, Jane Li,Tina Ok and Silvia Machat for their research and administrative support.Author ContributionsConceived and designed the experiments: EA KND KS. Performed theexperiments: KS. Analyzed the data: AS. Wrote the paper: EA KAM PDAS KND KS. Wrote the first draft and integrated suggestions from allauthors: EA. Made significant contributions to the interpretation of thedata, drafting of the manuscript: EA KAM PD AS KND KS. Approvedthe final manuscript: EA KAM PD AS KND KS.References1. Stockman JK, Lucea MB, Campbell JC (2013) Forced sexual initiation, sexualintimate partner violence and HIV risk in women: a global review of theliterature. AIDS Behav 17: 832–847. doi:10.1007/s10461-012-0361-4.2. 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