Drug involvement variations in overdose death spikes: county-level analysis in Massachusetts.

Background: Communities often experience relatively quiet periods disrupted by sudden surges of drug overdoses, suggesting that the risk of death can change substantially in a short period. Multiple substances are often involved in overdoses, and it is crucial to understand which are more frequently observed in spikes. This study aimed to investigate the involvement of specific substances in overdose spikes at the state and county levels in Massachusetts. Methods: We applied a spike detection method to identify daily spikes among 9915 overdose fatalities in Massachusetts from 2020 to 2023. A day was identified as a spike if the number of overdose deaths was over two SDs of the adjusted moving average with a lag of 30 days. We used a general linear mixed model to compare the presence of cocaine, psychostimulants, fentanyl, heroin and prescription opioids in overdose deaths between spike and typical days. Finally, we analysed and compared the results for 8 of the 14 counties in Massachusetts with the highest maximum overdose deaths per day. Results: At the state level from 2020 to 2023, no substances showed significant differences in spike and typical days. Cocaine was more prevalent in multiple counties during spikes. Fentanyl-involved overdose deaths were common on typical days in two counties. Psychostimulants were more prevalent on spike and typical days depending on the county. Heroin and prescription opioids only showed differences in one county each. Conclusion: Our analysis shows high heterogeneity of involved substances in overdose death spikes across counties in Massachusetts. This heterogeneity reinforces the need for localised response strategies. This understanding can guide more targeted local resource allocation and inform strategies to improve public health practices, ultimately aiming to reduce the impact of future overdose spikes.