The potential role of wastewater surveillance signals for overdose prevention in Marin County, California, February 2023-June 2024.

Wastewater surveillance (WWS), a public health tool used primarily for infectious diseases in the U.S., might have expanded applications in select settings for substance use. Drug overdose is a leading cause of premature death across the US and in Marin County, California. In 2023, Marin County piloted a WWS program to detect fentanyl, norfentanyl (a fentanyl metabolite), xylazine, cocaine, and methamphetamine and evaluate its potential use in an Overdose Alert System. A mixed-methods study was implemented to assess correlations between substance concentrations in wastewater and emergency medical service (EMS) encounters for nonfatal opioid overdoses and overdose deaths and the acceptability of WWS for overdose prevention. Spearman's rho rank correlation and unadjusted Poisson regression models were used to evaluate associations between wastewater measures and overdoses. Norfentanyl wastewater levels were correlated with EMS confirmed opioid overdoses one and three weeks later (ρ = 0.39, p < 0.001), and associated with a 16% increase in fentanyl-involved fatal drug overdoses three weeks later (IRR = 1.16, 95% CI: 1.10-1.21). Over half of respondents supported WWS for overdose alerts. Among respondents at an increased risk of witnessing or experiencing an overdose, 39% reported that they would take action if wastewater showed presence of a new drug or a spike in levels. Respondents also indicated concerns about privacy, and potential changes in policing resulting from WWS. Jurisdictions might consider setting population size sampling limits and data sharing guidelines when using WWS. WWS could be useful in community-based settings for primary prevention and early intervention planning and complement other surveillance methods.