The impact of neighbourhood-level marginalization on risk of opioid overdose: a population-based retrospective cohort study

Objectives — To investigate the association between neighbourhood-level dimensions of marginalization and risk of opioid overdose in Ontario, Canada.

Methods — We conducted a retrospective cohort study from January 1st, 2016 to December 31st, 2022 using population-level administrative data. Neighbourhood-level marginalization was measured by three dimensions (households and dwellings, material resources, and age and labour force) of the Ontario Marginalization Index. Fatal and non-fatal overdoses were extracted using ICD-10 codes. Modified (robust) Poisson regression using Generalized Estimating Equations produced risk ratios (RRs) to assess the association between neighbourhood-level marginalization and overdose while adjusting for relevant confounders.

Results — A random sample of 1,904,556 individuals was taken from all eligible Ontarians (n = 10,806,807). A total of 7,523 overdoses occurred within the observation period, 1,879 (25%) of which were fatal. The rates of all overdose and fatal overdose were 599.35 and 149.48 events per 1,000,000 person years, respectively. In multivariate models comparing all marginalization quintiles to the lowest quintile, neighbourhood residential instability, material resources, and age and labour force were significantly associated with increased risk of all overdose, as well as non-fatal and fatal overdose specifically. Residential instability showed a stronger association with fatal overdose than non-fatal overdose, whereas material resources showed a stronger association with risk of non-fatal overdose than fatal overdose in higher marginalization quintiles.

Conclusion — Neighbourhood-level marginalization is significantly associated with risk of overdose, fatal or non-fatal. This relationship is seen independently of income and demographic factors. Addressing social disadvantage should be made a priority amidst the ongoing opioid crisis.