Overdose as a complex contagion: modelling the community spread of overdose events following law enforcement efforts to disrupt the drug market.

Background: The opioid overdose mortality crisis in the USA is an ongoing public health epidemic. Ongoing law enforcement strategies to disrupt local unregulated drug markets can have an iatrogenic effect of increasing overdose by driving consumers towards new suppliers with unpredictable drug products of unknown potency.

Methods: Cross-sectional study using point-level information on law enforcement opioid-related drug seizures from property room data, opioid-related non-fatal overdose events from emergency medical services and block group-level social determinants of health data from multiple sources. Using an endemic-epidemic spatiotemporal regression model, we estimated the degree to which exposure to drug supply disruptions triggers future overdose events within small space-time distances in Indianapolis, Indiana.

Results: Neighbourhoods with more structural racism, economic deprivation or urban blight were associated with higher rates of non-fatal overdose. Exposure to an opioid-related drug seizure event had a significant and positive effect on the epidemic probability of non-fatal overdose. An opioid seizure that occurred within 250 m and 3 days, 250 m and 7 days, and 250 m and 14 days of an overdose event increased the risk of a new non-fatal overdose by 2.62 (rate ratio (RR)=2.62, 95% CI 1.87 to 3.67), 2.17 (RR=2.17, 95% CI 1.87 to 2.59) and 1.83 (RR=1.83, 95% CI 1.66 to 2.02), respectively. Similar spatiotemporal patterns were observed in a smaller spatial bandwidth.

Conclusions: Results demonstrated that overdoses exhibit a community spread process, which is exacerbated following law enforcement strategies to disrupt the unregulated drug market. We discuss decriminalisation and increasing resources that promote safer drug use to combat this public health crisis.