A quantitative bias analysis of the association between supervised consumption service use and sharing of injection equipment among people who inject drugs in Toronto, Canada

Purpose

Supervised consumption services (SCS) prevent fatal overdoses, but less is known about their contemporary impact on infectious disease risk.

Methods

We used quantitative bias analyses (QBA) to evaluate the association between SCS use and sharing of injection equipment while accounting for measurement error, selection bias, and unmeasured confounding, drawing on a cross-sectional sample of 695 people who inject drugs in Toronto, Canada surveyed from 2018 to 2020. We estimated the association between self-reported SCS use and equipment sharing using modified Poisson regression. Sensitivity analyses varied SCS use categories and definitions of sharing. QBA estimated the impact of misclassification, selection bias, and unmeasured confounding.

Results

Almost all participants (96.6 %) had recently used a needle and syringe program. Frequent SCS use (≥26 % of injections) was not associated with sharing equipment (adjusted prevalence ratio (aPR): 0.98; 95 % CI: 0.77–1.24). Results of sensitivity analyses did not meaningfully differ. In multiple bias analysis, the median bias-adjusted PR of 1.04 (range: 0.83–1.42) suggested no association between regular SCS use (≥75 % of injections) and syringe sharing.

Conclusions

In summary, SCS use was not associated with equipment sharing in a context of high needle and syringe program coverage. Misclassification, selection bias, and unmeasured confounding did not appear to impact the observed associations.