Illicit Fentanyl Use and Hepatitis C Virus Seroconversion Among People Who Inject Drugs in Tijuana and San Diego: Results From a Binational Cohort Study.

BACKGROUND: Illicitly manufactured fentanyl (IMF) increases overdose mortality, but its role in infectious disease transmission is unknown. We examined whether IMF use predicts hepatitis C virus (HCV) and human immunodeficiency virus (HIV) incidence among a cohort of people who inject drugs (PWID) in San Diego, California and Tijuana, Mexico. METHODS: PWID were recruited during 2020-2022, undergoing semi-annual interviewer-administered surveys and HIV and HCV serological rapid tests through 2024. Cox regression was conducted to examine predictors of seroconversion considering self-reported IMF use as a 6-month lagged, time-dependent covariate. RESULTS: Of 398 PWID at baseline, 67% resided in San Diego, 70% were male, median age was 43 years, 42% reported receptive needle sharing, and 25% reported using IMF. HCV incidence was 14.26 per 100 person-years (95% confidence interval [CI]: 11.49-17.02), and HIV incidence was 1.29 (95% CI: .49-2.10). IMF was associated with HCV seroconversion, with a univariable hazard ratio (HR) of 1.64 (95% CI: 1.09-2.40), and multivariable HR of 1.57 (95% CI: 1.03-2.40). The direction of the relationship with HIV was similar, albeit not significant (HR 2.39; 95% CI: .66-8.64). CONCLUSIONS: We document a novel association between IMF and HCV seroconversion among PWID in Tijuana-San Diego. Few HIV seroconversions (n = 10) precluded our ability to assess if a similar relationship held for HIV. IMF's short half-life may destabilize PWID-increasing the need for repeat dosing and sharing smoking materials and syringes. New preventive care approaches may reduce HCV transmission in the fentanyl era.

Long-acting Injectable PrEP Interest and General PrEP Awareness among People who Inject Drugs in the San Diego-Tijuana Border Metroplex.

Long-acting injectable HIV pre-exposure prophylaxis (LAI-PrEP) could help overcome multilevel challenges to HIV prevention for people who inject drugs (PWID), including those in the binational San Diego-Tijuana metroplex. Yet, general PrEP awareness and interest in LAI-PrEP remain underexplored among PWID. From 2020 to 2021, 562 HIV-negative PWID in San Diego and Tijuana completed surveys assessing general PrEP awareness and interest in oral and LAI-PrEP. Modified Poisson regression examined factors associated with general PrEP awareness. Multinomial logistic regression assessed factors associated with interest in both oral and LAI-PrEP, oral PrEP only, LAI-PrEP only, or neither. General PrEP awareness was low (18%) and associated with experiencing unsheltered homelessness (adjusted prevalence ratio [APR] = 1.50, 95% confidence interval [CI]: 0.96-2.33), past 6-month fentanyl injection (APR = 1.53, 95% CI: 1.04-2.25), and transactional sex (APR = 1.71, 95% CI: 1.06-2.76). Interest in oral PrEP only was most common (44%), followed by LAI-PrEP only (25%) and neither (16%). Compared to the odds of being interested in LAI-PrEP only, the odds of being interested in oral PrEP only were lower among those who were stopped by police (AOR = 0.38, 95% CI: 0.22-0.65), reported past 6-month fentanyl injection (AOR = 0.33, 95% CI: 0.20-0.56), polydrug use (AOR = 0.48, 95% CI: 0.27-0.86), injecting multiple times daily (AOR = 0.26, 95% CI: 0.14-0.46), receptive syringe use (AOR = 0.30, 95% CI: 0.19-0.49), and higher perceived HIV risk (AOR = 0.24, 95% CI: 0.15-0.39). Interest in LAI-PrEP was more common among PWID reporting social and structural factors that could interfere with oral PrEP adherence, suggesting LAI-PrEP implementation could increase PrEP coverage among those most vulnerable to HIV.

Safe Injection Self-Efficacy is Associated with HCV and HIV Seropositivity Among People Who Inject Drugs in the San Diego-Tijuana Border Region.

Safe injection self-efficacy (SISE) is negatively associated with injection risk behaviors among people who inject drugs (PWID) but has not been examined in differing risk environments. We compared responses to a validated SISE scale between PWID in San Diego, California and Tijuana, Mexico, and examine correlates of SISE among PWID in Tijuana. PWID were recruited via street outreach for a longitudinal cohort study from October 2020-September 2021. We compared SISE scale items by city. Due to low variability in SISE scores among San Diego residents, we restricted analysis of factors associated with SISE to Tijuana residents and identified correlates of SISE score levels (low, medium, high) using ordinal logistic regression. Of 474 participants, most were male (74%), Latinx (78%) and Tijuana residents (73%). Mean age was 44. Mean SISE scores among San Diego residents were high (3.46 of 4 maximum) relative to Tijuana residents (mean: 1.93). Among Tijuana residents, White race and having previously resided in San Diego were associated with higher SISE scores. HCV and HIV seropositivity, homelessness, fentanyl use, polysubstance co-injection, and greater injection frequency were associated with lower SISE scores. We found profound inequalities between Tijuana and San Diego SISE, likely attributable to differential risk environments. Associations with fentanyl and polysubstance co-injection, injection frequency, and both HIV and HCV seropositivity suggest that SISE contribute to blood-borne infection transmission risks in Tijuana. SISE reflects an actionable intervention target to reduce injection risk behaviors, but structural interventions are required to change the risk environment.

RESUMEN: La autoeficacia de inyección segura (SISE, por sus siglas en inglés) se asocia negativamente con conductas de riesgo de inyección entre las personas que se inyectan drogas (PWID, por sus siglas en inglés), pero no se ha examinado en diferentes entornos de riesgo. Comparamos las respuestas a una escala validada de SISE entre PWID en San Diego, California, y Tijuana, México, y examinamos los correlatos de SISE entre PWID en Tijuana. Participantes fueron reclutados por medio de alcance callejero para un estudio de cohorte longitudinal entre octubre 2020 ­septiembre de 2021. Comparamos los ítems de la escala SISE por ciudad. Debido a la baja variabilidad en los puntajes SISE entre los residentes de San Diego, restringimos el análisis de factores asociados con SISE a los residentes de Tijuana e identificamos factores correlacionados con niveles de SISE (bajo, medio, alto) mediante regresión logística ordinal. De 474 participantes, la mayoría eran hombres (74%), latinx (78%) y residentes de Tijuana (73%). La edad promedio fue de 44 años. Los puntajes medios de SISE entre los residentes de San Diego fueron altos (3.46 de un máximo de 4) en comparación con los residentes de Tijuana (media: 1.93). Entre los residentes de Tijuana, la raza blanca y haber residido previamente en San Diego se asociaron con puntajes más altos de SISE. La seropositividad para HCV y VIH, la falta de vivienda, el uso de fentanilo, la co-inyección de múltiples sustancias y una mayor frecuencia de inyecciónes se asociaron con puntajes más bajos de SISE. Encontramos profundas desigualdades entre SISE en Tijuana y San Diego, probablemente atribuibles a diferentes entornos de riesgo. Las asociaciones con fentanilo y la co-inyección de múltiples sustancias, la frecuencia de inyección y la seropositividad tanto para VIH como para HCV sugieren que SISE contribuye a los riesgos de transmisión de infecciones transmitidas por la sangre en Tijuana. SISE refleja un objetivo de intervención accionable para reducir las conductas de riesgo de inyección, pero se requieren intervenciones estructurales para cambiar el entorno de riesgo.

Water, sanitation, and hygiene access among people who inject drugs in Tijuana and San Diego in 2020-2021: a cross-sectional study.

BACKGROUND: Water, sanitation, and hygiene (WASH) access is critical to public health and human dignity. People who inject drugs (PWID) experience stigma and structural violence that may limit WASH access. Few studies have assessed WASH access, insecurity, and inequities among PWID. We describe WASH access, social and geographic inequalities, and factors associated with WASH insecurity among PWID in the Tijuana-San Diego metropolitan area. METHODS: In this cross-sectional binational study, we interviewed PWID (age 18+) in 2020-2021 about WASH access and insecurity. City of residence (Tijuana/San Diego) and housing status were considered as independent variables to describe key WASH access outcomes and to assess as factors associated with WASH insecurity outcomes. Measures of association between outcomes and independent variables were assessed using log modified-Poisson regression models adjusting for covariates. RESULTS: Of 586 PWID (202 Tijuana; 384 San Diego), 89% reported basic access to drinking water, 38% had basic hand hygiene, 28% basic sanitation, and 46% access to bathing, and 38% reported recent open defecation. Participants residing in Tijuana reported significantly higher insecurity in accessing basic drinking water (aRR: 1.68, 95%CI: 1.02-2.76), basic hygiene (aRR: 1.45, 95%CI: 1.28-1.64), and bathing (aRR: 1.21, 95%CI: 1.06-1.39) than those living in San Diego. Participants experiencing unsheltered homelessness experienced significantly higher insecurity in accessing basic drinking water (aRR: 2.03, 95%CI: 1.07-3.86), basic sanitation (aRR: 1.68, 95%CI: 1.48, 1.92), bathing (aRR: 1.84, 95%CI: 1.52-2.22), and improved water sources for cleaning wounds (aRR: 3.12, 95%CI: 1.55-6.29) and for preparing drugs (aRR: 2.58, 95%CI: 1.36-4.89) than participants living in permanent housing. CONCLUSION: WASH access among PWID in the Tijuana-San Diego metropolitan area was low by international standards and lower than the national averages in both countries. Homelessness was significantly associated with WASH insecurity in this population. Concentrated efforts are needed to guarantee continuously available WASH services for PWID-especially those who are unsheltered.

WaSH insecurity and anxiety among people who inject drugs in the Tijuana-San Diego border region.

BACKGROUND: Water, sanitation, and hygiene (WaSH) insecurity increases the risk of water-related diseases. However, limited research has been conducted on psychosocial distress as it relates to WaSH insecurity, especially among people who inject drugs (PWID). We examined the relationship between WaSH insecurity and related anxiety among PWID living in different housing conditions along the US-Mexico border region. METHODS: From 2020-2021, a cross-sectional study was conducted among 585 people who injected drugs within the last month in Tijuana (N = 202), San Diego (N = 182), and in both Tijuana and San Diego (N = 201). Participants underwent interviewer-administered surveys related to WaSH access, substance use, and generalized anxiety disorder (GAD-7). Quasi-Poisson regressions were used to assess associations between WaSH insecurity and anxiety in the prior 6-months. RESULTS: Participants were 75% male, 42% were unhoused and 91% experienced WaSH insecurity in the prior 6-months. After adjusting for housing status, gender, and age, lack of access to basic drinking water (Adj RR: 1.28; 95% CI: 1.02-1.58), sanitation (Adj RR:1.28; 95% CI: 1.07-1.55), and a daily bath/shower (Adj RR: 1.38; 95% CI: 1.15-1.66) were associated with mild-severe anxiety. The number of WaSH insecurities was independently associated with a 20% increased risk of experiencing anxiety per every additional insecurity experienced (Adj RR: 1.20; CI: 1.12-1.27). We also found a significant interaction between gender and housing status (p = 0.003), indicating that among people experiencing sheltered/unsheltered homelessness, women had a higher risk of mild-severe anxiety compared to men (Adj RR: 1.55; 95% CI: 1.27-1.89). At the same time, among women, those who are unhoused have 37% increased risk of anxiety than those who live in stable housing conditions (Adj RR: 1.37; 95% CI: 1.01-1.89). CONCLUSION: The lack of specific WaSH services, particularly lack of drinking water, toilets, and daily showers were associated with higher levels of anxiety among PWID in the Tijuana-San Diego border region. Women experiencing homelessness were especially vulnerable. WaSH interventions that provide safe, 24-h access may help to reduce anxiety and health risks associated with WaSH insecurity.

Willingness to use and distribute HIV self-testing kits among people who inject drugs in the San Diego-Tijuana border region.

BACKGROUND: HIV self-testing (HIVST) could increase HIV testing access among people who inject drugs (PWID), and secondary distribution (i.e., peer-delivery) of HIVST kits in PWID social networks could further expand coverage. We assessed willingness to use and distribute HIVST kits among PWID in the San Diego-Tijuana border region. METHODS: From 2020 to 2021, HIV-negative PWID in San Diego, USA, and Tijuana, Mexico, completed surveys and provided data on individual (N = 539) and social network (N = 366) characteristics. We used modified Poisson regression to examine the effects of individual and social network characteristics on willingness to use and distribute HIVST kits. RESULTS: Most participants were willing to use (81%) and distribute (81%) HIVST kits. At the individual level, prior HIV testing was positively associated with willingness to use (adjusted prevalence ratio [aPR] = 1.24, 95% confidence interval [CI] 1.10-1.40) and distribute (aPR = 1.27, 95% CI 1.12-1.43) HIVST kits, while perceiving oneself to be at higher HIV risk than others was negatively associated with willingness to use HIVST kits (aPR = 0.83, 95% CI 0.74-0.93). At the network level, willingness to distribute HIVST kits was positively associated with network size (aPR = 1.04 per member, 95% CI 1.01-1.08) and greater proportions of one's network encouraging them to use drugs (aPR = 1.29, 95% CI 1.16-1.44) and having a history of homelessness (aPR = 1.51, 95% CI 1.31-1.74) or detention/arrest (aPR = 1.57, 95% CI 1.36-1.82), and negatively associated with a greater proportion of one's network including "very close" persons (aPR = 0.80, 95% CI 0.69-0.94). CONCLUSIONS: We found high potential for HIVST kits and their secondary distribution to increase HIV testing among PWID who face the greatest barriers to facility-based testing.

Health, harm reduction, and social service providers' perspectives on the appropriateness and feasibility of peer distribution of HIV self-test kits among people who use drugs.

BACKGROUND: People who use drugs (PWUD) experience elevated HIV risk and numerous barriers to facility-based HIV testing. HIV self-testing (HIVST) could circumvent many of those barriers and is acceptable among PWUD, yet HIVST implementation for PWUD is limited. Service providers' perspectives on specific HIVST delivery strategies could help increase availability for PWUD. METHODS: From April-November 2021, we interviewed 16 health, harm reduction, and social service providers working with PWUD in San Diego, CA. Interviews and rapid thematic analysis explored perspectives on HIVST's utility and appropriateness, as well as the feasibility of and anticipated challenges with specific HIVST delivery strategies, including peer or secondary distribution. RESULTS: Participants viewed HIV as a significant threat to PWUD health and confirmed the presence of numerous barriers to local facility-based HIV testing. Participants viewed HIVST as a promising and potentially empowering solution. Based on community familiarity with secondary distribution of harm reduction supplies (i.e., naloxone) and information, participants viewed secondary distribution of HIVST kits as an appropriate and feasible strategy for increasing the reach of HIVST, but also described potential barriers (e.g., engaging socially disconnected individuals, ensuring linkages to services following HIVST) and provided suggestions for alternative HIVST kit delivery models (e.g., harm reduction vending machines). CONCLUSIONS: Service providers viewed secondary distribution of HIVST kits among PWUD as promising, appropriate, and feasible, yet specialized efforts may be needed to reach the most marginalized individuals and ensure consistent provision of educational information and referral supports that maximize the impact of this approach.

Preliminary Efficacy of a Theory-Informed Intervention to Increase COVID-19 Testing Uptake Among People Who Inject Drugs in San Diego County: Findings From a Pilot Randomized Controlled Trial.

BACKGROUND: People who inject drugs (PWID) have low rates of COVID-19 testing yet are vulnerable to severe disease. In partnership with a mobile syringe service program (SSP) in San Diego County, CA, we developed the evidence-, community-, and Social Cognitive Theory-informed "LinkUP" intervention (tailored education, motivational interviewing, problem-solving, and planning) to increase COVID-19 testing uptake among PWID. PURPOSE: To assess preliminary efficacy of LinkUP in increasing PWID COVID-19 testing in a pilot randomized controlled trial (RCT). METHODS: We referred participants (PWID, ≥18 years old, San Diego County residents who had not recently undergone voluntary COVID-19 testing) to mobile SSP sites that had been randomized (by week) to offer the active LinkUP intervention or didactic attention-control conditions delivered by trained peer counselors. Following either condition, counselors offered on-site rapid COVID-19 antigen testing. Analyses estimated preliminary intervention efficacy and explored potential moderation. RESULTS: Among 150 participants, median age was 40.5 years, 33.3% identified as Hispanic/Latinx, 64.7% were male, 73.3% were experiencing homelessness, and 44.7% had prior mandatory COVID-19 testing. The LinkUP intervention was significantly associated with higher COVID-19 testing uptake (p < .0001). Homelessness moderated intervention effects; LinkUP increased COVID-19 testing uptake more among participants experiencing homelessness (adjusted risk ratio [aRR]: 1.80; 95% CI: 1.56-2.09; p < .0001) than those not experiencing homelessness (aRR: 1.20; 95% CI: 1.01-1.43; p = .04). CONCLUSIONS: Findings from this pilot RCT support the preliminary efficacy of the "LinkUP" intervention to increase COVID-19 testing among PWID and underscore the importance of academic-community partnerships and prevention service delivery through SSPs and other community-based organizations serving vulnerable populations.

People who inject drugs (PWID) are vulnerable to severe COVID-19 disease yet have low rates of COVID-19 testing. We partnered with a syringe service program (SSP) in San Diego County, CA, to develop "LinkUP," an evidence- and community-informed intervention. Specifically, LinkUP used tailored education, motivational interviewing, and problem-solving and planning strategies to increase COVID-19 testing uptake among PWID. This study was a pilot randomized controlled trial (RCT) designed to assess the preliminary efficacy of LinkUP in increasing PWID COVID-19 testing. We referred participants (PWID, ≥18 years old, San Diego residents without recent voluntary COVID-19 testing) to mobile SSP sites that had been randomized (by week). Trained peer counselors then offered LinkUP or an educational control condition lasting the same length (~30 minutes). After either condition, counselors offered on-site rapid COVID-19 antigen testing. Among 150 participants, our analyses found that the LinkUP intervention was associated with higher COVID-19 testing uptake, especially for participants experiencing homelessness. In summary, our findings from this pilot RCT support the preliminary efficacy of the "LinkUP" intervention in increasing COVID-19 testing among PWID. This study also underscores the importance of academic-community partnerships and prevention service delivery through SSPs and other community-based organizations serving vulnerable populations.

Network-level HIV risk norms are associated with individual-level HIV risk and harm reduction behaviors among people who inject drugs: a latent profile analysis.

The COVID-19 related U.S.-Mexico border-crossing restrictions disrupted social networks and HIV harm reduction services among people who inject drugs (PWID) in San Diego and Tijuana. We assessed associations of descriptive network norms on PWID's HIV vulnerability during this period. Between 10/2020 and 10/2021, 399 PWID completed a behavioral and egocentric questionnaire. We used Latent Profile Analysis to categorize PWID into network norm risk profiles based on proportions of their network (n = 924 drug use alters) who injected drugs and engaged in cross-border drug use (CBDU), among other vulnerabilities. We used logistic and linear regressions to assess network profile associations with individual-level index of HIV vulnerability and harm reduction behaviors. Fit indices specified a 4-latent profile solution of descriptive network risk norms: lower (n = 178), moderate with (n = 34) and without (n = 94) CBDU and obtainment, and higher (n = 93). Participants in higher risk profiles reported more HIV vulnerability behaviors and fewer harm reduction behaviors. PWID's gradient of HIV risk was associated with network norms, warranting intervention on high-vulnerability networks when services are limited.

Correlates of Coronavirus Disease 2019 (COVID-19) Vaccine Hesitancy Among People Who Inject Drugs in the San Diego-Tijuana Border Region.

BACKGROUND: People who inject drugs (PWID) are vulnerable to acquiring severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We examined correlates of coronavirus disease 2019 (COVID-19) vaccine hesitancy among PWID in the US-Mexico border region, of whom only 7.6% had received ≥ 1 COVID-19 vaccine dose by September 2021. METHODS: Between October 2020 and September 2021, participants aged ≥ 18 years from San Diego, California, USA, and Tijuana, Baja California, Mexico, who injected drugs within the last month completed surveys and SARS-CoV-2, human immunodeficiency virus (HIV), and hepatitis C virus (HCV) serologic testing. Logistic regressions with robust standard error estimation via generalized estimating equations identified factors associated with being unsure or unwilling to receive COVID-19 vaccines. RESULTS: Of 393 participants, 266 (67.7%) were willing to receive COVID-19 vaccines and 127 (32.3%) were hesitant (23.4% unwilling and 8.9% unsure). Older participants, those with greater food insecurity, and those with greater concern about acquiring SARS-CoV-2 were more willing to be vaccinated. Higher numbers of chronic health conditions, having access to a smart phone or computer, and citing social media as one's most important source of COVID-19 information were independently associated with vaccine hesitancy. COVID-19-related disinformation was independently associated with vaccine hesitancy (adjusted odds ratio: 1.51 per additional conspiracy theory endorsed; 95% confidence interval: 1.31-1.74). CONCLUSIONS: Nearly one third of people injecting drugs in the US-Mexico border region were COVID-19 vaccine hesitant, which was significantly associated with exposure to social media, disinformation and co-morbidities and inversely associated with food security and high perceived threat of COVID-19. Interventions that improve accurate knowledge of and trust in COVID-19 vaccines are needed in this vulnerable population.

A cross-sectional study of factors associated with COVID-19 testing among people who inject drugs: missed opportunities for reaching those most at risk.

BACKGROUND: People who inject drugs (PWID) are vulnerable to SARS-CoV-2 infection. We examined correlates of COVID-19 testing among PWID in the U.S.-Mexico border region and described encounters with services representing potential opportunities (i.e., 'touchpoints') where COVID-19 testing could have been offered. METHODS: Between October, 2020 and September, 2021, participants aged ≥18 years from San Diego, California, USA and Tijuana, Baja California, Mexico who injected drugs within the last month completed surveys and SARS-CoV-2, HIV, and HCV serologic testing. Logistic regression identified factors associated with COVID-19 testing including potential touchpoints, comorbidities and COVID-19 related misinformation and disinformation. RESULTS: Of 583 PWID, 30.5% previously had a COVID-19 test. Of 172 PWID who tested SARS-CoV-2 seropositive (30.1%), 50.3% encountered at least one touchpoint where COVID-19 testing could have been offered within the prior six months. Factors independently associated with at least two fold higher odds of COVID-19 testing were living in San Diego, recent incarceration, receiving substance use treatment, and experiencing ≥1 chronic health condition. Homelessness, having received ≥1 dose of COVID-19 vaccine, and having a HIV or HCV test since the COVID-19 epidemic began were also independently associated with having had a prior COVID-19 test. CONCLUSION: We identified several factors independently associated with COVID-19 testing and multiple touchpoints where COVID-19 testing could be scaled up for PWID, such as SUD treatment programs and syringe service programs. Integrated health services are needed to improve access to rapid, free COVID-19 testing in this vulnerable population.

Changes in injecting versus smoking heroin, fentanyl, and methamphetamine among people who inject drugs in San Diego, California, 2020 to 2023.

Background: Amidst a rapidly evolving drug supply in North America, people who inject drugs may be transitioning to smoking them. We aimed to assess changes in injecting and smoking heroin, fentanyl and methamphetamine among a cohort of people who injected drugs at baseline from San Diego, California. Methods: Over five six-month periods spanning October 2020-April 2023, we assessed prevalence of injecting and smoking opioids or methamphetamine and whether participants used these drugs more frequently by smoking than injecting. Multivariable Poisson regression via Generalized Estimating Equations was used to examine time trends. Results: Of 362 participants, median age was 40 years; most were male (72%), non-Hispanic (55%), and unhoused (67%). Among this cohort, of whom 100% injected (or injected and smoked) at baseline, by period five (two years later), 34% reported only smoking, while 59% injected and smoked, and 7% only injected. By period five, the adjusted relative risk (aRR) of injecting opioids was 0.41 (95% Confidence Interval [CI]: 0.33, 0.51) compared to period one, and the aRR for injecting methamphetamine was 0.50 (95% CI: 0.39, 0.63). Compared to period one, risks for smoking fentanyl rose significantly during period three (aRR=1.44, 95% CI: 1.06, 1.94), four (aRR=1.65, 95% CI: 1.24, 2.20) and five (aRR=1.90, 95% CI: 1.43, 2.53). Risks for smoking heroin and methamphetamine more frequently than injecting these drugs increased across all periods. Conclusions: Opioid and methamphetamine injection declined precipitously, with notable increases in smoking these drugs. Research is urgently needed to understand the health consequences of these trends.

Changes in injecting versus smoking heroin, fentanyl, and methamphetamine among people who inject drugs in San Diego, California, 2020-2023.

BACKGROUND: Amidst an increasingly toxic drug supply in North America, people who inject drugs may be transitioning to smoking them. We aimed to assess changes in injecting and smoking opioids and methamphetamine among a cohort of people who inject drugs from San Diego, California. METHODS: Over five six-month periods spanning October 2020-April 2023, we assessed prevalence of injecting and smoking opioids or methamphetamine and whether participants used these drugs more frequently by smoking than injecting. Multivariable Poisson regression via generalized estimating equations was used to examine time trends. RESULTS: Of 362 participants, median age was 40 years; a minority were female (29%), Hispanic/Latinx/Mexican (45%), and housed (33%). Among this cohort, of whom 100% injected (and 84% injected and smoked) in period one (October 2020-April 2021), by period five (November 2022-April 2023), 34% only smoked, 59% injected and smoked, and 7% only injected. By period five, the adjusted relative risk (aRR) of injecting opioids was 0.41 (95% Confidence Interval [CI]: 0.33, 0.51) and the aRR for injecting methamphetamine was 0.50 (95% CI: 0.39, 0.63) compared to period one. Risks for smoking fentanyl rose significantly during period three (aRR=1.44, 95% CI: 1.06, 1.94), four (aRR=1.65, 95% CI: 1.24, 2.20) and five (aRR=1.90, 95% CI: 1.43, 2.53) compared to period one. Risks for smoking heroin and methamphetamine more frequently than injecting these drugs increased across all periods. CONCLUSIONS: Opioid and methamphetamine injection declined precipitously, with notable increases in smoking these drugs. Research is needed to understand the health consequences of these trends.

Water, sanitation and hygiene insecurity predict abscess incidence among people who inject drugs in a binational US-Mexico metropolitan area: A longitudinal cohort study.

INTRODUCTION: People who inject drugs (PWID) are at high risk of developing injection-related infections, including abscesses. Access to water, sanitation, and hygiene (WASH) are key human rights and services; yet these services have been underexplored as predictors of abscesses among PWID. METHODS: Longitudinal analysis was employed among a cohort of PWID to determine if WASH insecurity (lack of access) was associated with abscess incidence in the Tijuana, Mexico and San Diego, United States metropolitan area during 24-months of follow-up survey data from 2020 to 2023. We calculated abscess prevalence at baseline and tracked the incidence of new abscesses among individuals without an abscess during the previous visit. Time dependent Cox regression modeling was employed with variance clustered by participant to characterize the relationship between WASH insecurity and abscess incidence. RESULTS: At baseline, hand hygiene insecurity, bathing insecurity in the previous six months and open defecation in the last week, were reported by 60 %, 54 % and 38 % of participants, respectively; 21 % reported an abscess in the last six months. The incidence of abscesses was 24.4 (95 %CI: 21.1-27.6) per 100 person-years. After adjusting for covariates, the hazard of developing an abscess remained significantly elevated among individuals using non-improved (with risk of contamination) water sources (e.g., surface water) for preparing drugs (adjusted HR [adjHR]: 1.49 [95 %CI: 1.01-2.21], experiencing bathing insecurity (adjHR: 1.59 [95 %CI: 1.12-2.24]) and open defecation (adjHR: 1.65 [95 %CI: 1.16-2.35]). CONCLUSIONS: PWID in the Tijuana-San Diego metropolitan area reported facing high rates of insecurity accessing WASH services. Abscess incidence was higher (four to nine times) than observed rate among PWID cohorts in other settings. Access to continuously available toilet facilities, bathing infrastructure, and safe water sources for preparing drugs for injection could prevent abscesses among PWID. Accessible WASH infrastructure should be ensured among PWID communities and promoted as a key component of harm reduction infrastructure.

Safe Injection Self-Efficacy is associated with HCV and HIV seropositivity among people who inject drugs in the San Diego-Tijuana border region.

Background: Safe injection self-efficacy (SISE) is negatively associated with injection risk behaviors among people who inject drugs (PWID) but has not been examined in differing risk environments. We compared responses to a validated SISE scale between PWID in San Diego, California and Tijuana, Mexico, and examine correlates of SISE among PWID in Tijuana. Methods: PWID were recruited via street outreach for a longitudinal cohort study from October 2020 - September 2021. We compared SISE scale items by city. Due to low variability in SISE scores among San Diego residents, we restricted analysis of factors associated with SISE to Tijuana residents and identified correlates of SISE scores (low, medium, high) using ordinal logistic regression. Results: Of 474 participants, most were male (74%), Latinx (78%) and Tijuana residents (73%). Mean age was 44. Mean SISE scores among San Diego residents were high (3.46 of 4 maximum) relative to Tijuana residents (mean: 1.93). Among Tijuana residents, White race and having previously resided in San Diego were associated with higher SISE scores. HCV and HIV seropositivity, homelessness, fentanyl use, polysubstance co-injection, and greater injection frequency were associated with lower SISE scores. Conclusions: We found profound inequalities between Tijuana and San Diego SISE, likely attributable to differential risk environments. Associations with fentanyl and polysubstance co-injection, injection frequency, and both HIV and HCV seropositivity suggest that SISE contribute to blood-borne infection transmission risks in Tijuana. SISE reflects an actionable intervention target to reduce injection risk behaviors, but structural interventions are required to intervene upon the risk environment.

HIV-1 transmission dynamics among people who inject drugs on the US/Mexico border during the COVID-19 pandemic: a prosepective cohort study.

Background: We examined HIV prevalence and transmission dynamics among people who inject drugs in the U.S./Mexico border region during the COVID-19 pandemic. Methods: People who inject drugs aged ≥18 years from 3 groups were recruited: people who inject drugs who live in San Diego (SD) and engaged in cross-border drug use in Tijuana, Mexico (SD CBDUs), and people who inject drugs in SD and Tijuana (TJ) who did not engage in cross-border drug use (NCBDUs). We computed HIV prevalence at baseline and bivariate incidence-density rates (IR) at 18-month follow-up. Bayesian phylogenetic analysis was used to identify local transmission clusters, estimate their age, and effective reproductive number (Re) over time within the clusters. Findings: At baseline (n = 612), 26% of participants were female, 9% engaged in sex work, and HIV prevalence was 8% (4% SD CBDU, 4% SD NCBDU, 16% TJ NCBDU). Nine HIV seroconversions occurred over 18 months, IR: 1.357 per 100 person-years (95% CI: 0.470, 2.243); 7 in TJ NCBDU and 2 in SD CBDU. Out of 16 identified phylogenetic clusters, 9 (56%) had sequences from both the U.S. and Mexico (mixed-country). The age of three youngest mixed-country dyads (2018-2021) overlapped with the COVID-related US-Mexico border closure in 2020. One large mixed-country cluster (N = 15) continued to grow during the border closure (Re = 4.8, 95% Highest Posterior Density (HPD) 1.5-9.1) with 47% engaging in sex work. Interpretation: Amidst the COVID-19 pandemic and the border closure, cross-border HIV clusters grew. Efforts to end the HIV epidemic in the U.S. should take into account cross-border HIV-1 transmission from Tijuana. Mobile harm reduction services and coordination with municipal HIV programs to initiate anti-retroviral therapy and pre-exposure prophylaxisis are needed to reduce transmission. Funding: This research was supported by the James B. Pendleton Charitable Trust and the San Diego Center for AIDS Research.

A brief instrument measuring the water, sanitation and hygiene domain of menstrual health among women who inject drugs.

BACKGROUND: Domains of adequate menstrual health (MH) include access to water, sanitation, and hygiene (WASH). People who menstruate with social disadvantages-such as homelessness or drug injection practices-often face barriers to WASH access. However, validated instruments to measure MH are limited among marginalized populations, and available instruments involve lengthy surveys. We developed and evaluated psychometric properties of a novel 'MH WASH Domain Scale-12' among people who menstruate and who inject drugs in the Tijuana-San Diego region and identified correlates of MH access using this scale. METHODS: We constructed a MH-scale based on access to twelve WASH-related items: (1) menstrual products, (2) body hygiene (bathing per week), (3) water sources for bathing, (4) improved, (5) non-shared, (6) available, (7) private, (8) nearby, (9) and safe sanitation facilities, (10) availability of soap, (11) water source for handwashing, and (12) handwashing facilities with soap/water. Variables were dichotomized and summed, with scores ranging from 0-12 points and higher scores indicating better MH access. We assessed the scale's reliability and construct and content validity using data from a binational cross-sectional study. The sample included people who inject drugs (PWID) who had ever menstruated in their lifetime and were 18+ during 2020-2021. MH-WASH items were described, and the scale was further used as an outcome variable to identify correlates. RESULTS: Among 125 (124 cis-female and 1 trans-male) PWID that reported menstruating, our 'MH WASH Domain Scale-12' was reliable (Cronbach's alpha = 0.81, McDonald's Omega total = 0.83) and valid. We identified two sub-domains: Factor-1 included items describing 'WASH availability' and Factor-2 contained items related to 'WASH security'-encompassing physical and biological safety. Scale scores were significantly lower among participants experiencing unsheltered homelessness compared to participants experiencing sheltered homelessness or living in permanent housing. CONCLUSION: We constructed and validated a novel and reliable scale to measure MH-related WASH access that can be used to assess MH among marginalized populations in English- and Spanish-speaking contexts. Using this scale we identified disparities in MH-WASH access among PWID and who menstruate in the US-Mexico border region.

Predictors of COVID-19 vaccine uptake among people who inject drugs.

INTRODUCTION: We studied characteristics of COVID-19 vaccination uptake among people who inject drugs (PWID). METHODS: Participants aged ≥18 years who injected drugs ≤1 month ago were recruited into a community-based cohort from October 2020 to September 2021 in San Diego, California Poisson regression identified correlates of having had ≥1 COVID-19 vaccine dose based on semi-annual follow-up interviews through March 15, 2022. RESULTS: Of 360 participants, 74.7% were male, mean age was 42 years; 63.1% were Hispanic/Mexican/Latinx. More than one-third had ≥1 co-morbidity. HIV and HCV seroprevalence were 4.2% and 50.6% respectively; 41.1% lacked health insurance. Only 37.8% reported having ≥1 COVID-19 vaccine dose. None received ≥3 doses. However, of those vaccinated, 37.5% were previously unwilling/unsure about COVID-19 vaccines. Believing COVID-19 vaccines include tracking devices (adjusted incidence rate ratio [aIRR]: 0.62; 95% CI: 0.42,0.92) and lacking health insurance (aIRR: 0.60; 95% CI: 0.40,0.91) were associated with approximately 40% lower COVID-19 vaccination rates). Ever receiving influenza vaccines (aIRR: 2.16; 95%CI: 1.46, 3.20) and testing HIV-seropositive (aIRR: 2.51; 95% CI: 1.03, 6.10) or SARS-CoV-2 RNA-positive (aIRR: 1.82; 95% CI: 1.05, 3.16) independently predicted higher COVID-19 vaccination rates. Older age, knowing more vaccinated people, and recent incarceration were also independently associated with higher COVID-19 vaccination rates. CONCLUSIONS: One year after COVID-19 vaccines became available to U.S. adults, only one third of PWID had received ≥1 COVID-19 vaccine dose. Multi-faceted approaches that dispel disinformation, integrate public health and social services and increase access to free, community-based COVID-19 vaccines are urgently needed.

A Brief Peer-Led Intervention to Increase COVID-19 Vaccine Uptake Among People Who Inject Drugs in San Diego County: Results From a Pilot Randomized Controlled Trial.

Background: We evaluated the impact of a brief peer-led intervention on COVID-19 vaccination among people who inject drugs (PWID) presenting at syringe services program (SSP) locations in San Diego County, California. Methods: Between March and July 2022, PWID aged ≥18 years without recent voluntary COVID-19 testing who were not up to date on COVID-19 vaccinations received a single-session motivational interviewing intervention (LinkUP) or an attention-matched didactic control condition from trained peer counselors at SSP sites randomized by week. Following either 30-minute session, counselors offered referrals to local vaccination services. Multivariable log binomial regression via generalized estimating equations assessed LinkUP effects on (1) acceptance of COVID-19 vaccination referrals immediately postintervention and (2) COVID-19 vaccine uptake at 6-month follow-up. Results: COVID-19 vaccination outcomes were obtained on 135 (90.6%) of 149 participants. In multivariable analysis, participants receiving LinkUP had greater acceptance of COVID-19 vaccination referrals than controls (adjusted relative risk, 3.50; 95% CI, 1.01-12.2) and were marginally more likely to report receiving a new COVID-19 vaccine dose (adjusted relative risk, 1.57; 95% CI, .99-2.48). After 6 months, 20% reported receiving a new vaccine dose; however, if COVID-19 vaccine had been available at SSPs, this proportion could have been as high as 34.3% (45.3% LinkUP vs 24.3% control; P = .01). Conclusions: A brief peer-led SSP-based intervention significantly improved COVID-19 vaccination among PWID. Further improvements could likely be obtained by supporting SSPs to offer COVID-19 vaccination on-site instead of relying on referrals. Clinical Trials Registration: ClinicalTrials.gov NCT05181657.

"A lotta people switched playing hard ball to playing Russian roulette": Experiences with rising overdose incidence caused by drug supply changes during the COVID-19 pandemic in the San Diego-Tijuana border metroplex.

Background: People who use drugs (PWUD) in the San Diego, USA and Tijuana, Mexico metroplex face high overdose risk related to historic methamphetamine use and relatively recent fentanyl introduction into local drug supplies. The personal overdose experiences of PWUD in this region are understudied, however, and may have been influenced by the COVID pandemic. Methods: From September-November 2021, we conducted 28 qualitative interviews among PWUD ≥18 years old sampled from an ongoing cohort study in the San Diego-Tijuana metroplex. Interviews explored overdose experiences and changes in the drug supply. Thematic analysis of coded interview transcripts explored overdose experiences, perspectives on drug supply changes, interactions with harm reduction services, and naloxone access. Results: Among 28 participants, 13 had experienced an overdose. Participants discussed rising levels of fentanyl in local drug supplies and increasing overdose incidents in their social networks. Participants discussed a general shift from injecting heroin to smoking fentanyl in their networks. Participants' most common concerns included having consistent access to a safe and potent drug supply and naloxone. Conclusion: Participants prioritized adapting to drug supply changes and preventing overdose compared to other health concerns, such as HIV and COVID-19. Efforts to address overdose in this region could benefit from drug checking services and expanded, equitable delivery of naloxone.