Wastewater surveillance as an early warning indicator for norovirus: Validating wastewater signals against clinical indicators in British Columbia, Canada, 2021-2025.

BACKGROUND: Norovirus is the leading cause of acute gastroenteritis globally and causes significant morbidity. Despite this, norovirus is not reportable to the public health system in most jurisdictions, making it challenging to detect and control local transmission. Wastewater-based epidemiology is a potential tool for narrowing this gap, allowing for non-invasive, population-level surveillance. OBJECTIVE: In this study, it assess wastewater-based epidemiology as a surveillance tool for monitoring norovirus in British Columbia, Canada, by comparing norovirus wastewater signals to norovirus-related hospital admissions and genogroup I (GI)-related emergency department (ED) visits. METHODS: More than six thousand (n=6,167) wastewater samples from 12 municipal treatment plants were collected between January 10, 2021-September 27, 2025 and pooled to generate a population-weighted average for the province. Norovirus hospital admissions and GI-related ED visits were extracted for the same period from the Discharge Abstract Database and the National Ambulatory Care Reporting System, respectively, and were compared with wastewater signals using time-lagged cross-correlation analyses. RESULTS: Time-lagged cross-correlation analyses indicate significant positive correlation overall between unadjusted norovirus wastewater concentrations and norovirus hospitalizations (Spearman's ρ=0.69, p<0.01) and GI-related ED visits (Spearman's ρ=0.84, p<0.01), with wastewater leading hospitalizations by two weeks (Spearman's ρ=0.71) and aligned with ED visits (Spearman's ρ=0.83). CONCLUSION: The findings support the validity of using wastewater-based epidemiology for monitoring norovirus at the population-level and suggest that it may provide an early warning signal for severe norovirus activity requiring hospitalization, prompting a more timely response.