Gender differences in hepatitis C virus incidence in and out of opioid agonist treatment among people who inject drugs in Montréal, Canada, March 2011 – March 2024

<b>Background</b>: <br/>Some evidence suggests the benefits of opioid agonist therapy (OAT) in preventing hepatitis C virus (HCV) acquisition are stronger in men than women. However, existing analyses have used crude OAT exposure measures. We compared HCV incidence and estimated the effects of OAT on HCV acquisition among women and men who inject drugs using granular OAT exposure data. <br/><br/><b>Methods</b>: <br/>Data were from Montréal’s Hepatitis Cohort (HEPCO) study, March 2011-March 2024. We estimated overall and gender-stratified HCV incidence rates and performed discrete-time survival analyses, overall and gender-stratified, to estimate the associations between OAT engagement and HCV acquisition. In multivariable analyses, we adjusted for age and incarceration. <br/><br/><b>Results</b>: <br/>HCV incidence was similar in women and men, with a rate of 6.93 (95% CI 5.67, 8.46) per 100 p-y in men, and 7.84 (95% CI 5.13, 11.98) per 100 p-y in women. In the men’s adjusted model of the association between OAT engagement and HCV acquisition (in OAT versus not in OAT (but eligible)), the aHR was 0.52 (95% CI 0.33, 0.83). Among women, the aHR was 0.89 (95% CI 0.30, 2.70). However, the confidence interval was wide and crossed the null in the women’s model. <br/><br/><b>Conclusion</b>: <br/>We found similar HCV incidence among women and men who inject drugs in Montréal; however, among OAT-eligible men, OAT engagement was strongly associated with a lower risk of HCV acquisition. These findings highlight that gender disparities in HCV, as observed in some settings, are not consistent. Further research is needed to determine factors underlying gender differences.