The evolving drug epidemic of prescription opioid injection and its association with HCV transmission among people who inject drugs in Montréal, Canada.

Aims: To examine temporal trends in prescription opioid (PO) injection and to assess its association with hepatitis C virus (HCV) seroconversion among people who inject drugs (PWID).

Design: Prospective cohort study spanning 2004 to 2016. Setting: Montréal, Canada. Participants: PWID reporting injection during the past 6 months. Measurements: PWID were recruited between 2004 and 2016. At each 3-6-month follow-up visit, participants completed interview-administered questionnaires and were tested for HCV-antibody. Findings: Among 1524 PWID [83% males, mean age 38 years, standard deviation (SD) = 10, 34% (31-36) prescription opioid (PO) injection past month] included in trends analyses, PO injection use expanded between 2004 and 2009, and plateaued between 2010 and 2016 (trend tests < 0.001 and 0.335, respectively). Of the 432 HCV-seronegative PWIDs followed at least once (81% males, mean age 34, SD 9.8, 38% injection PO), 153 became HCV-antibody-positive during 1230 years of follow-up, for an incidence of 12.4 per 100 person-years [95% confidence interval (CI) = 10.6, 14.6]. PO injectors were 3.9 times more likely to seroconvert to HCV, relative to non-PO injectors. In a multivariate analysis, a stronger association between PO injection and HCV seroconversion was found post-2009 [adjusted hazard ratio (aHR) = 5.4, 95% CI = 2.7, 10.8] than before (aHR = 1.5, 95% CI = 0.9, 2.4) (P-value for interaction = 0.001).

Conclusion: Prescription opioid injection increased among people who inject drugs in Montréal, Canada from 2004 to 2009, to reach a plateau between 2010 and 2016. The association between prescription opioid injection and HCV seroconversion was stronger during the second period than the first according to the epidemic phase.