Latent polydrug use patterns and the provision of injection initiation assistance among people who inject drugs in three North American settings.

INTRODUCTION: We sought to identify latent profiles of polysubstance use patterns among people who inject drugs in three distinct North American settings, and then determine whether profile membership was associated with providing injection initiation assistance to injection-naïve persons. METHODS: Cross-sectional data from three linked cohorts in Vancouver, Canada; Tijuana, Mexico; and San Diego, USA were used to conduct separate latent profile analyses based on recent (i.e., past 6 months) injection and non-injection drug use frequency. We then assessed the association between polysubstance use patterns and recent injection initiation assistance provision using logistic regression analyses. RESULTS: A 6-class model for Vancouver participants, a 4-class model for Tijuana participants and a 4-class model for San Diego participants were selected based on statistical indices of fit and interpretability. In all settings, at least one profile included high-frequency polysubstance use of crystal methamphetamine and heroin. In Vancouver, several profiles were associated with a greater likelihood of providing recent injection initiation assistance compared to the referent profile (low-frequency use of all drugs) in unadjusted and adjusted analyses, however, the inclusion of latent profile membership in the multivariable model did not significantly improve model fit. DISCUSSION AND CONCLUSIONS: We identified commonalities and differences in polysubstance use patterns among people who inject drugs in three settings disproportionately impacted by injection drug use. Our results also suggest that other factors may be of greater priority when tailoring interventions to reduce the incidence of injection initiation. These findings can aid in efforts to identify and support specific higher-risk subpopulations of people who inject drugs.

Gender and the first-time provision of injection initiation assistance among people who inject drugs across two distinct North American contexts: Tijuana, Mexico and Vancouver, Canada.

INTRODUCTION: Injection drug use initiation is commonly facilitated by other people who inject drugs (PWID). We investigated how the gender of PWID influences their risk of providing initiation assistance to others across two distinct geo-cultural settings. METHODS: Data were drawn from two prospective cohorts in Tijuana, Mexico and Vancouver, Canada which conducted semi-annual interviews within the PReventing Injecting by Modifying Existing Responses (PRIMER) study. Participants consisted of PWID who had reported never providing injection initiation assistance at baseline. We then conducted site-specific discrete-time survival analyses assessing the relationship between gender and other relevant covariates (e.g. age and past 6-month sex work) on the risk of the first reported instance of providing initiation assistance. RESULTS: Of 1988 PWID (Tijuana: n = 596; Vancouver: n = 1392), 256 (43%) and 511 (36.7%) participants were women, and 42 (1.7%) and 78 (1.6%) reported recent injection initiation assistance across a median of three and two follow-up visits, respectively. Women had a lower risk of providing injection initiation assistance for the first time in Tijuana (adjusted hazard ratio = 0.52, 95% confidence interval 0.27-0.99), but not in Vancouver. Gendered pathways, like sex work, were associated with providing initiation assistance for the first time in Vancouver (adjusted hazard ratio = 1.97, 95% confidence interval 1.08-3.61). DISCUSSION AND CONCLUSIONS: Women in Tijuana, but not Vancouver, were less likely to provide first-time initiation assistance among PWID. These results can inform gender- and site-specific prevention efforts aimed at reducing transitions into drug injecting across geographic contexts.

Involvement of people who inject drugs in injection initiation events: a cross-sectional analysis identifying similarities and differences across three North American settings.

OBJECTIVES: People who inject drugs (PWID) play an integral role in facilitating the entry of others into injection drug use (IDU). We sought to assess factors influencing PWID in providing IDU initiation assistance across three distinct North American settings and to generate pooled measures of risk. DESIGN: We employed data from three PWID cohort studies participating in PReventing Injecting by Modifying Existing Responses (PRIMER), for this cross-sectional analysis. SETTING: Tijuana, Mexico; San Diego, USA; Vancouver, Canada. PARTICIPANTS: A total of 2944 participants were included in this study (Tijuana: n=766, San Diego: n=353, Vancouver: n=1825). MEASUREMENTS: The outcome was defined as recently (ie, past 6 months) assisting in an IDU initiation event. Independent variables of interest were identified from previous PRIMER analyses. Site-specific multiple modified Poisson regressions were fit. Pooled relative risks (pRR) were calculated and heterogeneity across sites was assessed via linear random effects models. RESULTS: Evidence across all three sites indicated that having a history of providing IDU initiation assistance (pRR: 4.83, 95% CI: 3.49 to 6.66) and recently being stopped by law enforcement (pRR: 1.49, 95% CI: 1.07 to 2.07) were associated with a higher risk of providing assistance with IDU initiation; while recent opioid agonist treatment (OAT) enrolment (pRR: 0.64, 95% CI: 0.43 to 0.96) and no recent IDU (pRR: 0.21, 95% CI: 0.07 to 0.64) were associated with a lower risk. We identified substantial differences across site in the association of age (I2: 52%), recent housing insecurity (I2: 39%) and recent non-injection heroin use (I2: 78%). CONCLUSION: We identified common and site-specific factors related to PWID's risk of assisting in IDU initiation events. Individuals reporting a history of assisting IDU initiations, being recently stopped by law enforcement, and recently injecting methamphetamine/speedball were more likely to have recently assisted an IDU initiation. Whereas those who reported not recently engaging in IDU and those recently enrolled in OAT were less likely to have done so. Interventions and harm reduction strategies aimed at reducing the harms of IDU should incorporate context-specific approaches to reduce the initiation of IDU.

The impact of recent homelessness on the provision of injection drug use initiation assistance among persons who inject drugs in Tijuana, Mexico and Vancouver, Canada.

OBJECTIVE: To assess the relationship between experiencing homelessness and assisting injection drug use (IDU) initiation among people who inject drugs (PWID) in Tijuana, Mexico and Vancouver, Canada. METHODS: We used self-reported questionnaire data collected semi-annually on PWID from Tijuana (n = 703) and Vancouver (n = 1551) between 2014 and 2017. Within each setting, the effect of recent (i.e., past six months) homelessness on recent provision of injection initiation assistance (i.e., helping anybody inject for the first time in the past six months) was estimated using inverse-probability-of-treatment (IPT)-weighted estimation of a marginal structural model. RESULTS: Across follow-up, the prevalence of recent homelessness at a given visit ranged from 11.6%-16.5% among Tijuana-based participants and 9.4%-18.9% among Vancouver-based participants; the prevalence of recent provision of injection initiation at a given follow-up visit was lower, ranging from 3.3%-5.4% in Tijuana and 2.5%-4.1% in Vancouver. Based on the IPT-weighted estimates, recent homelessness was associated with 66% greater odds among Tijuana-based PWID (Adjusted Odds Ratio [AOR] = 1.66; 95% CI: 1.01-2.73) and 47% greater odds among Vancouver-based PWID (AOR = 1.47, 95% CI: 1.02-2.13) of providing injection initiation assistance over the same six-month period. CONCLUSION: We found that recently experiencing homelessness was associated with an increased likelihood of PWID reporting IDU initiation assistance over time in both Tijuana and Vancouver. Addressing homelessness may decrease the initiation of IDU via multiple pathways.

Self-perception of assisting with future injection drug initiation: The influence of relationships in the process of drug injecting initiation.

INTRODUCTION AND AIMS: People who inject drugs (PWID) play critical roles in assisting others into injection drug use (IDU) initiation. Understanding perceptions of PWID's risk of initiating others is needed to inform interventions for prevention. The objective was to examine factors associated with self-perception of assisting with future IDU initiation events. The primary variables of interest are the relationships of PWID with the person(s) they assisted and their reasons for previously providing initiation assistance. DESIGN AND METHODS: Data from Preventing Injecting by Modifying Existing Responses, a multi-site prospective community-recruited cohort study, were analysed. Analyses were restricted to PWID who reported ever providing IDU initiation assistance. Site-specific (Vancouver, Canada [n = 746]; San Diego, USA [n = 95] and Tijuana, Mexico [n = 92]) multivariable logistic regression analyses were performed to determine factors associated with self-perception of assisting with future IDU initiation. RESULTS: Having provided IDU initiation assistance to a family member or intimate partner decreased the odds of self-perception of assisting with future IDU initiation in Vancouver (AOR = 0.4; 95% CI 0.2-0.8); however, previous IDU initiation assistance to an 'other' increased the odds of self-perception of assisting with future IDU in Tijuana (AOR = 12.0; 95% CI 2.1-70.3). Daily IDU (Vancouver: AOR = 3.7; 95% CI 2.1-6.4) and less than daily IDU (San Diego: AOR = 5.9; 95% CI 1.3-27.1) (Vancouver: AOR = 2.6; 95% CI 1.4-2.9) were associated with increased self-perception of assisting with future IDU compared to current non-injectors. DISCUSSION AND CONCLUSIONS: Relationship to past initiates and IDU frequency might increase PWID's self-perception of assisting with future IDU. Interventions focused on social support and reducing IDU frequency may decrease occurrences of IDU initiation assistance.

Opioid agonist treatment and the process of injection drug use initiation.

BACKGROUND: Opioid agonist treatment (OAT) is an effective biomedical intervention to manage opioid use disorder among persons who inject drugs (PWID). Preliminary evidence suggests that OAT may also disrupt the social communicability of injection drug use (IDU) practices by established PWID. We therefore aim to investigate the association between OAT enrollment and initiating others into IDU among PWID in Vancouver, Canada. METHODS: Preventing Injecting by Modifying Existing Responses (PRIMER; NIDA DP2-DA040256-01) is a prospective multi-cohort study seeking to identify structural interventions that reduce the risk that PWID initiate others into IDU. The present analysis was conducted using data from a participating cohort of PWID in Vancouver, Canada, between December 2014 and May 2017. Multivariable logistic regression models were built to assess the association between reporting active (i.e., within the past six months) OAT enrollment and assisting others in injection initiation. A final model was determined using a manual stepwise approach whereby covariates were excluded if their removal altered the coefficient of interest by <5%. RESULTS: Participants (n = 1740) were predominantly male (62.3%); 35.1% reported daily injecting (n = 611); 860 (49.4%) reported active OAT enrollment, and 80 (4.6%) reported recently providing injection initiation assistance. In a multivariable model, participants who reported active OAT enrollment had significantly lower odds of recently providing injection initiation assistance (Adjusted Odds Ratio = 0.52, 95% Confidence Interval: 0.31-0.87, P = 0.01). CONCLUSION: Results suggest a protective association between OAT and the expansion of IDU practices among vulnerable populations, suggesting its potential use as 'addiction treatment as prevention.'

Gender differences in the provision of injection initiation assistance: a comparison of three North American settings.

AIM: Individuals experience differential risks in their initiation into drug injecting based on their gender. Data suggest women are more likely to be injected after their initiator and to share injection equipment. Little is known, however, regarding how gender influences the risk that people who inject drugs (PWID) may assist others into injection initiation. We therefore sought to investigate the role of "initiator" gender in the provision of injection initiation assistance across multiple settings. METHODS: We employed data from PReventing Injecting by Modifying Existing Responses (PRIMER), a multi-cohort study investigating factors influencing injection initiation assistance provision. Data were drawn from three cohort studies of PWID in San Diego, USA (STAHR II); Tijuana, Mexico (El Cuete IV); and Vancouver, Canada (VDUS). Site-specific logistic regression models were fit, with lifetime provision of injection initiation assistance as the outcome and gender as the independent variable. RESULTS: Overall, 3.2% (24/746) of the women and 4.6% (63/1367) of the men reported providing injection initiation assistance. In Tijuana, men were more than twice as likely to have provided injection initiation assistance after controlling for potential confounders (adjusted odds ratio = 2.17, 95% confidence interval: 1.22-3.84). Gender was not significantly associated with providing injection initiation assistance in other sites. CONCLUSION: We identified that being male in Tijuana, specifically, was associated with providing injection initiation assistance, which could inform targeted outreach aimed at reducing the influence of PWID populations on non-injectors in this site. This will likely require that existing interventions address gender- and site-specific factors for effectiveness.