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

Prescription opioid injection increased among people who inject drugs in Montréal, Canada from 2004 to 2009, to reach a plateau between 2010 and 2016. Prescription opioid 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).