Short and sporadic injecting cessation episodes as predictors of incident hepatitis C virus infection: findings from a cohort study of people who inject drugs in Montréal, Canada.

BACKGROUND AND AIMS: For most people who inject drugs (PWID), drug injecting follows a dynamic process characterized by transitions in and out of injecting. The objective of this investigation was to examine injecting cessation episodes of one- to three-month duration as predictors of hepatitis C virus (HCV) acquisition.

DESIGN: Cohort study.

SETTING: Montréal, Canada.

PARTICIPANTS: 372 HCV-uninfected (HCV RNA negative, HCV antibody positive or negative) PWID (mean age 39, 82% male, 45% HCV antibody positive) enrolled between March 2011 and June 2016.

MEASUREMENTS: At three-month intervals, participants completed an interviewer-administered questionnaire and were tested for HCV particles (HCV RNA). At each visit, participants indicated whether they injected in each of the past three months (defined as three consecutive 30-day periods). Injecting cessation patterns were evaluated on a categorical scale: persistent injecting (no injecting cessation in the past 3 months), sporadic injecting cessation (injecting cessation in 1/3 or 2/3 months), and short injecting cessation (injecting cessation in 3/3 months). Their association with HCV infection risk was examined using Cox regression analyses with time-dependent covariates, including age, gender, incarceration, opioid agonist treatment, and other addiction treatments.

FINDINGS: At baseline, 61%, 26%, and 13% of participants reported persistent injecting, sporadic injecting cessation, and short injecting cessation, respectively. HCV incidence was 7.5 per 100 person-years (95%CI 5.9-9.5; 916 person-years of follow-up). In adjusted Cox models, sporadic injecting cessation and short injecting cessation were associated with lower risks of incident HCV infection compared to persistent injecting [adjusted hazard ratios: 0.56 (95%CI 0.30-1.04) and 0.24 (95%CI 0.09-0.61), respectively].

CONCLUSION: Short and sporadic injecting cessation episodes were common among a cohort of people who inject drugs in Montréal, Canada. Injecting cessation episodes appear to be protective against hepatitis C virus acquisition, particularly when maintained for at least three months.