Correlations between wastewater levels of naloxone and substance use disorder treatment medications with treatment encounters and overdoses - Marin County, California, USA, March 2023-June 2024.

OBJECTIVES

We tested wastewater samples for buprenorphine, methadone, naltrexone, naloxone, and their metabolites to assess correlations with treatment encounters and overdoses.

STUDY

DESIGN

Correlation analysis at the weekly time step. Exposures were wastewater mass loads of buprenorphine, methadone, naltrexone, naloxone, and their metabolites. Outcomes were overdose deaths, medications for opioid use disorder (MOUD) treatment encounters, non-fatal overdose Emergency Medical Services (EMS) encounters same, one, and two weeks later.

METHODS

Wastewater samples collected twice weekly (February 2023-June 2024) were tested for each analyte. Weekly geometric means were generated and normalized by daily wastewater flow rate and population (mg/1000 people/day). Spearman's correlation coefficients were calculated between weekly counts for overdose deaths, OUD treatment encounters, non-fatal overdose EMS encounters, and wastewater mass loads (same, one, and two weeks later). Time series models, adjusting for monthly and quarterly seasonality, were used to assess trends in naloxone, methadone, and buprenorphine levels.

RESULTS

Higher naloxone levels were weakly (-0.2-0.3) associated with fewer overdose deaths two weeks later. Buprenorphine levels were positively associated with OUD treatment clients one week later (0.26; p = 0.03), and negatively correlated with EMS encounters for opioid overdose two weeks later (-0.32; p = 0.01). Weekly wastewater concentrations of naloxone and MOUDs significantly increased over time.

CONCLUSIONS

Wastewater surveillance for MOUDs and naloxone might aid in assessing treatment gaps and tracking progress towards overdose harm reduction and substance use disorder treatment goals. Correlations between increases in community-level buprenorphine levels and reduced overdoses highlight the importance of bolstering access to treatment.