Increased hepatitis C and HIV incidence among people who inject drugs in Montreal, Canada, 2011-2023

Background: Multiple sequelae of the COVID-19 pandemic, including disruptions to harm reduction services and reduced HCV treatment uptake, may have affected blood borne virus incidence among people who inject drugs (PWID). We aimed to estimate hepatitis C virus (HCV) and HIV incidence in PWID in Montreal, 2011-2023.

Method: The HEPCO study includes PWID aged ≥18 years and living in Montreal. Participants are interviewed every three months and provide blood samples for HIV and HCV testing. Data collection was halted March-November 2020, and was slow to recover. Significant efforts were launched in November 2022 to recruit new participants. We calculated HCV and HIV incidence for participants recruited March 2011-November 2023, who were HCV antibody negative or HCV antibody positive and RNA negative/HIV antibody negative at baseline, and had at least one follow-up interview. Annual incidence was calculated from 2011-2019, with data from January-February 2020 included in the 2019 estimate. Given extended follow-up times from March 2020-October 2022 (‘pandemic period’), this era was treated as one period of time. The period following the cohort relaunch (November 2022-November 2023; ‘post-pandemic’) was also treated as one period of time. For the post-pandemic period, we separately calculated incidence for participants recruited prior to this period, and newly recruited participants.

Results: HCV incidence peaked in 2014 at 12.5 per 100 person-years (PY; 95% CI: 8.7-17.5) and declined to 3.8 per 100PY (95% CI: 2.0-6.9) in 2019. It remained low during the pandemic period (1.7 per 100PY, 95% CI: 0.7-3.3), but rebounded in the post-pandemic period (10.7 per 100PY, 95% CI: 6.1-17.6). This rebound was observed in both long-time (9.3 per 100PY, 95% CI: 4.9-16.2) and newly recruited (32.2 per 100PY, 95% CI: 10.3-77.8) participants. HIV incidence during the pandemic period (0.2 per 100PY, 95% CI: 0.01-0.98) was similar to that prior to 2020 (0.2 per 100 person-years (PY); 95% CI: 0.08-0.4), but was higher during the post-pandemic period (1.4 per 100 PY, 95% CI: 0.2-4.5). None of the HIV infections in the post-pandemic period were in newly recruited participants.

Conclusion: HCV and HIV incidence have increased among PWID in Montreal. The HCV incidence trend likely reflects a multi-stage process, whereby the number of people susceptible to infection increased due to high treatment uptake prior to the pandemic, followed by a period of lower HCV treatment uptake and disrupted harm reduction service access during the pandemic. The specific mechanisms linked to increased HIV incidence need to be explored; HIV incidence in PWID has traditionally been very low in Montreal, but disruptions to harm reduction services may have been sufficient to lead to new infections. Confidence intervals around estimates for the post-pandemic period are wide due to limited observation time. Ongoing data collection will help to clarify incidence trends and causal mechanisms.