Detection of Measles Virus Genotype A in a Non-Endemic Wastewater Setting: Insights from Measles Wastewater and Environmental Monitoring in Canada's Capital Region.

The recent global resurgence of measles in 2023-2024, despite vaccine preventability, underscores a critical public health issue, largely due to reduced vaccination coverage during the SARS-CoV-2 pandemic. In response, Ottawa Public Health intensified vaccination efforts in 2023 and 2024. Additionally, a research initiative began in April 2024 to monitor Ottawa wastewater for measles virus (MeV) using established wastewater and environmental surveillance (WES) protocols. Unexpected positive MeV detections through RT-qPCR in Ottawa wastewater-despite no active regional cases-prompted genotypic and retrospective analyses of archived RNA samples dating back to 2020. The genotypic analysis identified positive detection to belong to genotype A, the progenitor strain of the viral vaccines, marking the first report of MeV vaccine RNA in a large catchment area. Linear regression analysis revealed detections aligned with intensified vaccination efforts by Ottawa Public Health. These findings emphasize the importance of integrating genotypic analysis into WES practices to mitigate possible confounding factors, such as vaccine shedding into wastewater. Additionally, this research highlights potential public health applications using MeV WES as a complementary tool. Implementing the findings of this study for MeV WES, and for other re-emerging viruses, could improve public health response and resource allocation.