A-Z Index × Submit A-Z Index × Submit A-Z Index Search Dropdown × Submit Facebook Twitter LinkedIn Syndicate Emerging Infectious Disease journal ISSN: 1080-6059 Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released.
The province of Ontario, Canada, experienced a major resurgent outbreak of measles in 2025. We conducted wastewater surveillance concurrently with clinical-based surveillance to track measles incidence in southwestern Ontario, adjacent to the United States. Measles virus (MeV) signal in wastewater was positively associated with clinical cases but did not provide early alert of changes in measles incidence when resolved by epidemiologic week. Assessment of virus partitioning showed MeV RNA was broadly distributed in the liquid phase but is most concentrated in the solids. We adapted an assay for differentiation of vaccine and wild-type MeV and used it to detect vaccine genotype measles after a vaccination campaign targeting underserved groups. We estimated MeV shedding in wastewater through sampling of sewer laterals serving a hospital treating measles infections. This outbreak is a case study in which we highlighted the use of wastewater surveillance for measles while supporting method development in real time.
Wastewater surveillance (WS) gained traction during the COVID-19 pandemic as an effective and unbiased means to track community infection complementary to clinical testing. Sampling a wastewater treatment plant (WWTP) or locations within a sewershed revealed infection hotspots and tracked genetic variants ( 1 ). Wastewater yielded high-quality whole-genome SARS-CoV-2 sequence data ( 2 ); it is a resource for tracking disease spread and a complement to clinical data to identify disease burden and routes of pathogen transmission ( 3 , 4 ). WS has extended to additional targets, including respiratory diseases ( 5 ), foodborne illness ( 6 ), and diseases of emerging concern, such as mpox and highly pathogenic avian influenza ( 7 – 9 ). Public health officials warned of the increased potential for outbreaks of vaccine-preventable diseases ( 10 ). COVID-19 pandemic–associated disruptions and vaccine misinformation affected immunization campaigns, including measles vaccination programs ( 11 ).
In 2025, Ontario experienced a large outbreak of measles; ≈2,400 confirmed cases were reported. Total cases nationwide reached 5,461 in 2025, positioning Canada as a hotspot for measles in North America ( 12 ). In November 2025, after 12 months of sustained transmission, Canada lost measles elimination status ( 13 ), a designation attained in 1998 ( 14 ). The 2025 outbreak of measles in Canada likely resulted from reduced vaccination coverage ( 15 ) and was the largest outbreak in 3 decades, overwhelming public health services, especially in southwestern Ontario, which experienced the highest caseload ( 16 ). Concurrent outbreaks in the US Southwest ( 17 ) and in Alberta, Canada ( 18 ), have raised interest in WS to complement clinical testing ( 19 ).
WS accounts for community members who might be hesitant to seek medical care ( 20 ); that characteristic is relevant to measles, considering most cases in North America have been linked to close-knit undervaccinated communities ( 21 , 22 ). Studies since 2025 have highlighted the application of WS to track measles at a community level ( 23 – 26 ) and assays that diffe…