| Sažetak: | <h4>Background and Aims</h4> <p>Understanding HCV transmission among people who inject drugs (PWID) is important for designing prevention strategies. This study aimed to investigate whether HCV infection among younger injectors occurs as a result of few or many transmission events from older injectors to younger injectorsamong PWID in cohorts recruited in Vancouver, Canada.</p> <h4>Methods</h4> <p>HCV antibody positive participants at enrolment or follow-up (1996-2012) were tested for HCV RNA and sequenced (Core-E2). Time-stamped phylogenetic trees were inferred using BEAST. Association of age with phylogeny was testedusing statistics implemented in the software BaTS. Factors associated with clustering (maximum cluster age: five years) were identified using logistic regression.</p> <h4>Results</h4> <p>Among 655 participants with HCV subtype 1a, 2b and 3a infection (26% female, 23% HIV+): 22% were younger (<27 years), and 11% had recent HCV seroconversion. When inferred cluster age was limited to <5 years, 15% (n=100) were in clusters/pairs.Although a moderate degree of segregation was observed between younger and older participants, there was alsotransmission between age groups. Younger age (<27 vs. >40, AOR: 3.01, 95% CI: 1.44, 6.29) and HIV infection (AOR: 1.73, 95%-CI: 1.06, 2.83) were independently associated with clustering.</p> <h4>Conclusions</h4> <p>In this population of PWID from Vancouver, HCV infection among young injectors was seeded from many transmission events between HCV-infected older injectors and younger injectors.Phylogenetic clustering was associated with younger age and HIV co-infection. These data suggest that HCV transmission among PWID is complex, with transmission occurring between and among older and younger PWID.</p>
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