Illicit Fentanyl Use Independently Predicts HCV Seroconversion Among a Cohort of People Who Inject Drugs in Tijuana and San Diego

BackgroundIllicitly manufactured fentanyl (IMF) increases overdose mortality, but its role in infectious disease transmission is unknown. We examined whether IMF use predicts HCV and HIV incidence among a cohort of people who inject drugs (PWID) in San Diego, CA and Tijuana, Mexico. MethodsPWID were recruited into a prospective cohort in two waves during 2020-2022, undergoing semi-annual interviewer-administered surveys, HIV and HCV serology through February 2024. Cox regression was conducted to examine predictors of seroconversion considering self-reported IMF use as a fixed or lagged, time-dependent covariate. ResultsOf 398 PWID at baseline, 67% resided in San Diego, 70% were male, median age was 43, 42% reported receptive needle sharing and 25% reported using IMF. Participants contributed a median of 6 semi-annual study visits (IQR:4-6). HCV incidence was 14.26 per 100 person-years (95% CI: 11.49-17.02), and HIV incidence was 1.29 (1.00-2.28). IMF was associated with HCV seroconversion, with a univariable hazard ratio (HR) of 1.68 (95%CI: 1.12-2.53) which remained significant in multivariable models (adjHR1.54; 95%CI:1.01-2.34). The direction of the relationship with HIV was similar, albeit not significant, with an HR of 2.53 (0.7-9.15). ConclusionWe document a novel association between IMF and HCV seroconversion among PWID in Tijuana-San Diego. There was insufficient power to detect if a similar relationship held for HIV. IMFs short half-life may destabilize PWID-- increasing the need for repeat dosing and sharing smoking materials and syringes. Tailoring medication dosing for opioid use disorder and new preventative care approaches may reduce HCV transmission in the fentanyl era. SummaryIn this cohort study of people who inject drugs in Tijuana, Mexico, and San Diego, California, fentanyl use was independently associated with HCV seroconversion. Tailored treatment and prevention efforts are needed for patients using fentanyl to minimize blood-borne infections.