Theme: Epidemiology & Public Health Research Year: 2018
Introduction: Opiate agonist therapy (OAT) is key in preventing hepatitis C virus (HCV)
transmission among people who inject drugs (PWID). Yet, little is known about the importance
of OAT dosage adequacy in shaping HCV infection risk. We investigated the joint association of
clinically-indicated and patient-perceived adequate OAT dosage levels with HCV infection risk
Methods: Data were drawn from a prospective cohort study of initially HCV RNA- (Ab+/-) PWID
(2004-2017). At 6/3-month intervals, participants were tested for HCV Ab/RNA and filled
behavioral questionnaires, self-reporting: current OAT enrolment (yes/no), their prescribed dose
(high dose defined as: ≥60mg/day if methadone; ≥16mg/day if buprenorphine) and perceived
dosage adequacy (adequate/inadequate). The exposure variable was a composite, five-level
measure: no OAT, OAT: high/adequate, high/inadequate, low/adequate and low/inadequate.
Cox regression analyses were fit adjusting for gender, injecting duration, housing, recent
incarceration and previous HCV infection among PWID eligible for OAT.
Results: Of 513 participants (median age: 35.0; 77.6% male), 168 acquired HCV over 1422.6
person-years (p-y) of follow-up [incidence: 11.8/100 p-y (95% CI: 9.5-12.9)]. For the 1589/3421
study visits where OAT was reported, 36.5%, 11.8%, 36.9% and 14.8% reported high/adequate,
high/inadequate, low/adequate and low/inadequate dosage, respectively. Compared to those
not on OAT, PWID prescribed a high OAT dose had a lower HCV risk if dosage was perceived
adequate [(aHR: 0.37 (0.18-0.77)], yet results were inconclusive if perceived inadequate [(aHR:
0.38 (0.12-1.21)]. Additionally, compared to those not on OAT, PWID prescribed a low OAT
dose had a similar HCV risk if dosage was perceived adequate [aHR: 1.08 (0.67–1.75)], and a
higher risk if perceived inadequate [aHR: 2.07 (1.22–3.52)].
Discussion: Our findings emphasize the importance of OAT dosage adequacy, both as
clinically-indicated and self-evaluated by PWID, in HCV prevention. Prevention strategies
should not rely solely on OAT access, and should consider the importance of dosage.
Disclosure of interest statement
AAA and NM are supported through a CanHepC PhD trainee scholarship. AAA is additionally
supported through a Canadian Institutes of Health Research PhD scholarship. JB has received
advisor fees from Gilead Sciences and Merck and a research grant from Gilead Sciences,
outside of this current work. None of the authors have commercial relationships that may pose a
conflict of interest in connection with this work.