Non-fatal overdose as a risk factor for subsequent fatal overdose among people who inject drugs

Objectives: To examine the relationship between non-fatal overdose and risk of subsequent fatal overdose. Methods: We assessed risk factors for overdose death among two prospective cohorts of persons who inject drugs (PWID) in Vancouver, Canada. Extended Cox regression was used to examine if reports of non-fatal overdose were associated with the time to fatal overdose while adjusting for other behavioral, social and structural confounders. Results: Between May, 1996 and December, 2011, 2317 individuals were followed for a median of 60.8 months. In total, 134 fatal overdose deaths were identified for an incidence density of 8.94 (95% confidence interval [CI]: 7.55-10.59) deaths per 1000 person-years. During the study period there were 1795 reports of non-fatal overdose. In a multivariate model, recent non-fatal overdose was independently associated with the time to overdose mortality (adjusted hazard ratio [AHR] = 1.95; 95% CI: 1.17-3.27). As well, there was a dose response effect of increasing cumulative reports of non-fatal overdose on subsequent fatal overdose. Conclusion: Reports of recent non-fatal overdose were independently associated with subsequent overdose mortality in a dose-response relationship. These findings suggest that individuals reporting recent non-fatal overdose should be engaged with intensive overdose prevention interventions. (C) 2016 Elsevier Ireland Ltd. All rights reserved.