UC San Diego

Background: Overdose and infectious disease are major causes of morbidity and mortality among people who use drugs (PWUD). Harm reduction is a public health approach to reducing the negative consequences of criminalized substance use. This dissertation explored access to and utilization of harm reduction practices and services among PWUD in Tijuana, Baja California, Mexico and San Diego, California, United States (U.S.).Methods: This dissertation utilized survey data from the La Frontera binational cohort study. Chapter 1 compared overdose prevention strategies utilized by PWUD in Tijuana (n=343) and San Diego (n=143) between May 2022–March 2023. Latent class analysis (LCA) identified underlying groups of PWUD based on their probabilities of utilizing these strategies. Chapter 2 compared Tijuana (n=345) and San Diego (n=129) participant scores on a safe injection self-efficacy (SISE) scale between October 2020–September 2021 and assessed correlates of SISE score levels using ordinal logistic regression. Chapter 3 assessed naloxone accessibility among PWUD in San Diego between December 2021–December 2022 using qualitative interviews (N=20) and survey data (N=194). Results: Chapter 1 revealed that participants’ primary overdose prevention strategies were trying to avoid fentanyl among Tijuana residents (84%) and trying to stop/reduce injecting among San Diego residents (52%). LCA revealed four latent classes among Tijuana participants characterized by unique overdose prevention strategies. Chapter 2 demonstrated that Tijuana residents had lower mean SISE scores than San Diego residents (1.93 vs. 3.46 out of 4). Among Tijuana participants, White race and previous San Diego residence were positively associated with greater SISE scores, whereas HCV and HIV seropositivity, homelessness, fentanyl use, polysubstance co-injection, and greater injection frequency were negatively associated. Chapter 3 showed that among PWUD in San Diego, 24% reported never having accessible naloxone, 52% sometimes did, and 24% always did. Qualitative findings revealed PWUD generally felt naloxone was easy to obtain in San Diego due to community distribution from harm reduction providers and satellite distribution among peers, but experienced some barriers. In quantitative analyses, greater naloxone accessibility was positively associated with female sex, witnessing an overdose, and knowing where to get free naloxone, while monthly income ≤USD$500 was negatively associated. Conclusions: These findings highlight multi-level opportunities to improve access to harm reduction services in Tijuana and San Diego, including drug checking, naloxone distribution and overdose response education, and medications for opioid use disorder (MOUD). Additionally, PWID in Tijuana could benefit from syringe service program (SSPs) expansion and safe injection self-efficacy education.