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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 1-3-month duration as predictors of hepatitis C virus (HCV) acquisition.


DESIGN
Cohort study.


SETTING
Montréal, Canada.


PARTICIPANTS
A total of 372 HCV-uninfected (HCV RNA-negative, HCV antibody-positive or -negative) PWID (mean age = 39.3 years, 82% male, 45% HCV antibody-positive) enrolled between March 2011 and June 2016.


MEASUREMENTS
At 3-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 3 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 of 3 or 2 of 3 months) and short injecting cessation (injecting cessation in 3 of 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% confidence interval (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 3 months.