Eight years of nationwide routine wastewater surveillance in New Zealand: Demonstrating its complementary role in public health policy

BACKGROUND AND AIMS: Monitoring illicit drug consumption is challenging due to its hidden and stigmatised nature. However, objective consumption data are essential for a wide range of stakeholders, including policy makers. Wastewater-based epidemiology (WBE) offers population-level consumption estimates, but in-depth discussion and application for routine monitoring has been limited. This study demonstrates the practical implementation of high spatio-temporal resolution WBE as a complementary public health surveillance tool. METHODS: 24-h composite influent wastewater samples (n = 23,158) were collected in New Zealand across 62 wastewater treatment plants between 2018 and 2025, representing around 80% of the New Zealand population. Per capita consumption (expressed in mg/day/1000 people) of methamphetamine, cocaine, MDMA, fentanyl and heroin was calculated. RESULTS: A marked nationwide surge in methamphetamine consumption was observed in influent wastewater in 2024, which ultimately contributed to the establishment of a Government action plan to combat methamphetamine harm in New Zealand. Similarly, a substantial increase in cocaine consumption was detected, with its use expanding from primarily urban and touristic centres to a widespread national distribution. A moderate rise in consumption was observed for MDMA, whereas no significant consumption trend changes were observed for fentanyl and heroin, with ongoing monitoring in place to enable a rapid response if necessary. CONCLUSIONS: WBE has become an integral component of New Zealand's public health surveillance infrastructure, serving as a data-driven tool for informing policymakers, understanding drug market dynamics, supporting harm reduction strategies, and enhancing toxicovigilance. Researchers play a crucial role in ensuring clear and targeted communication of results to non-specialist audiences to prevent over- or misinterpretation.