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