They don't know when the outbreak has plateaued in their region.
As measles spreads through more than 500 Canadians in the country's worst outbreak in over a decade, public health authorities find themselves navigating the crisis without a tool they themselves helped build. Wastewater surveillance — refined during the COVID-19 pandemic precisely for moments like this — sits largely idle, a casualty of bureaucratic handoffs and program cancellations. The outbreak, rooted in close-knit Mennonite and Anabaptist communities with lower vaccination rates, raises an older question in a new form: when the instruments of foresight exist, what does it mean to choose not to use them?
- More than 500 Canadians have contracted measles across southwestern Ontario and into Manitoba, making this the country's worst outbreak in over a decade — and case counts are still climbing.
- Infected individuals shed the virus four days before symptoms appear, meaning traditional surveillance is structurally blind to the outbreak's leading edge.
- Ontario shut down its provincial wastewater program last summer, deferring to federal authorities — but the federal dashboard does not monitor measles, leaving a surveillance gap no one has claimed responsibility for closing.
- One researcher at the University of Windsor is already testing southwestern Ontario wastewater for measles, not through any government mandate, but through informal local arrangements — a workaround that underscores the absence of coordinated action.
- The rural and religious communities at the heart of the outbreak fall almost entirely outside the national wastewater network's 74 reporting sites, leaving local public health units without the data they need to know whether the crisis is peaking or spreading.
More than 500 Canadians have contracted measles in the country's worst outbreak in over a decade, spreading through southwestern Ontario — Brant, Brantford, St. Thomas, Haldimand and Norfolk counties — and reaching Manitoba through family travel. Ontario's chief medical officer has traced the origin to a large Mennonite community gathering in New Brunswick last fall. The outbreak is disproportionately affecting Mennonite, Amish, and Anabaptist communities with lower vaccination rates. And yet public health authorities are responding without one of the most effective tools available to them.
That tool is wastewater surveillance — the testing of sewage for viral pathogens. During the COVID-19 pandemic, it proved quietly powerful: by reading what communities shed into the sewer system, officials could anticipate surges and deploy resources before hospitals felt the strain. It was held up as a model for future outbreak response. Measles, like COVID-19, spreads from people who aren't yet symptomatic — infected individuals begin shedding the virus roughly four days before any signs appear. That invisible window is exactly where wastewater testing could intervene, enabling faster vaccination drives and targeted outreach before a cluster becomes a crisis.
The reason it isn't being used is a story of institutional handoffs. Ontario cancelled its provincial wastewater program last summer, deferring to the Public Health Agency of Canada. But PHAC's national dashboard does not include measles — the agency tracks weekly case counts and classifies measles as a notifiable disease, a system that depends entirely on symptomatic patients being tested and reported. No plans exist to add measles to the wastewater monitoring work.
In the absence of federal or provincial action, one researcher has moved on his own. Mike McKay at the University of Windsor — who holds a formal PHAC agreement to test for COVID-19, influenza, and RSV — began measles wastewater testing in southwestern Ontario in February, through informal arrangements with local municipalities and a regional hospital. PHAC has not asked him to do so. A technical complication exists: the measles vaccine uses a live-attenuated virus that vaccinated people also shed, meaning a positive wastewater signal requires genetic sequencing to distinguish infection from recent vaccination. McKay calls it a solvable problem, but one that adds a few days to the process.
Coverage is the other constraint. PHAC's national network covers roughly 37 percent of the Canadian population across 74 sites — and the rural communities most affected by this outbreak fall almost entirely outside it. Local public health units, experts say, have no way of knowing whether the outbreak in their region has plateaued or is still growing. The infrastructure and expertise to change that exist. Whether the agencies responsible will choose to use them remains, for now, an open question.
More than 500 Canadians have now contracted measles in what has become the country's worst outbreak in over a decade. The virus has spread through southwestern Ontario — Brant, Brantford, St. Thomas, Haldimand County, Norfolk County — and has reached Manitoba through family visits. It traces back, according to a memo from Ontario's chief medical officer of health Dr. Kieran Moore, to a large gathering involving Mennonite communities in New Brunswick last fall. And yet, the public health system is navigating this surge largely in the dark, without a tool that experts say could have seen it coming.
That tool is wastewater surveillance — the practice of testing sewage samples for viral pathogens. During the COVID-19 pandemic, it became one of the more quietly effective instruments in the public health arsenal. By analyzing what communities were shedding into the sewer system, officials could map the virus's movement, anticipate surges, and deploy resources before hospitals felt the strain. At the time, it was widely described as a model for future outbreak response. Now, with measles spreading, experts are asking why it isn't being used.
The answer is complicated and, to some, maddening. Ontario — currently the epicenter of the outbreak — shut down its provincial wastewater surveillance program last summer, saying it would defer to the Public Health Agency of Canada, which runs a national monitoring dashboard. But PHAC's dashboard does not track measles. A spokesperson confirmed to CBC News that the agency monitors weekly case counts and posts them publicly, but that there are no plans to add measles to its wastewater monitoring work. The agency classifies measles as a nationally notifiable disease, which represents its highest tier of case-level tracking — but that system depends on symptomatic patients being tested and reported, not on catching the virus before anyone shows up at a clinic.
That gap matters because measles, like COVID-19, can spread from people who don't yet feel sick. Infected individuals begin shedding the virus roughly four days before any symptoms appear. That window — invisible to traditional surveillance — is precisely where wastewater testing could intervene. "We could identify the wastewater catchment areas where the measles virus might be spreading and then put in public health measures that would make a huge difference," said Eric Arts, a microbiology professor at Western University. In high-signal areas, he says, health authorities could accelerate vaccination drives or launch targeted education campaigns before a cluster becomes a crisis.
Mike McKay, director of the Great Lakes Institute for Environmental Research at the University of Windsor, has been doing this kind of work since the early days of the pandemic. His team holds a formal agreement with PHAC to test for COVID-19, influenza, and RSV. Last year, health officials in Detroit asked his team to begin weekly measles testing in their wastewater. By February of this year, McKay extended that work to southwestern Ontario — not through any federal or provincial mandate, but through informal arrangements with the municipality of Leamington, Windsor Regional Hospital, and the University of Windsor. PHAC, he said, has not asked him to test for measles.
There is a technical wrinkle that makes measles wastewater surveillance slightly more involved than testing for other viruses. The measles vaccine uses a live-attenuated form of the virus — weakened, harmless, but still shed into wastewater by recently vaccinated people. That means a positive signal in sewage could reflect either an active infection or a recent vaccination. Distinguishing between the two requires genetic sequencing, which currently adds a few days to the process. It's a solvable problem, McKay says, but it does require that extra step.
The other constraint is coverage. PHAC's national wastewater network, focused primarily on COVID-19, includes 74 reporting sites — enough to cover roughly 37 percent of the Canadian population. The communities most affected by the current measles outbreak, many of them rural and home to Mennonite, Amish, and other Anabaptist populations with lower vaccination rates, fall outside that network entirely. "The public health units in those regions just don't have access to this data," McKay said. "They don't know when the outbreak has plateaued in their region."
Arts is blunt about what Ontario's decision to cancel its program represents. The rationale, he said, made no sense — particularly given that wastewater surveillance is inexpensive and far less labor-intensive than contact tracing, which becomes increasingly unwieldy as case counts climb. A study published earlier this year out of the University of Ottawa found that measles detection through wastewater complements existing public health interventions rather than replacing them. The infrastructure, in other words, was built. The expertise exists. The question now is whether the agencies responsible for protecting public health will choose to use it.
Citas Notables
We could identify the wastewater catchment areas where the measles virus might be spreading and then put in public health measures that would make a huge difference.— Eric Arts, microbiology professor, Western University
We are essentially taking the pulse of the health of the community.— Mike McKay, director, Great Lakes Institute for Environmental Research, University of Windsor
La Conversación del Hearth Otra perspectiva de la historia
Why aren't health agencies just turning this on? The infrastructure was built during COVID.
Some of it was, yes — but Ontario dismantled its provincial program last summer, and the federal dashboard never added measles to what it tracks. There's a gap between the tool existing and anyone being assigned to run it for this specific virus.
Is this a funding problem or a priority problem?
Probably both, but the experts here lean toward priority. McKay's team is already doing the testing in Windsor through informal local agreements. The cost isn't the barrier — the decision to make it official hasn't been made.
What does it actually tell you that case counts don't?
It tells you what's circulating before people know they're sick. Measles sheds into wastewater four days before symptoms show. By the time someone tests positive and gets reported, they've already been contagious for nearly a week.
So the 500-case number is probably an undercount.
Almost certainly. Asymptomatic spread is real with measles, and the communities most affected — rural, with lower vaccination rates — aren't always connected to robust clinical surveillance either.
The outbreak traces back to a single gathering in New Brunswick. Could wastewater have caught it earlier?
That's the argument Arts and McKay are making. If the affected communities had active monitoring, public health might have seen viral load rising before the cluster was clinically visible and moved faster on vaccination campaigns.
What's the sequencing problem about?
The measles vaccine uses a weakened live virus, and vaccinated people shed it briefly. So a positive wastewater signal could mean an outbreak or just a recent vaccination drive. You need a few extra days of lab work to tell them apart.
That sounds manageable.
It is. It's a known limitation with a known solution. The delay is days, not weeks. The experts aren't saying it's a perfect tool — they're saying the tradeoff is worth it, especially now.
What would change if PHAC added measles to its dashboard tomorrow?
Coverage would still be the problem. The network hits about 37 percent of the population, and the hardest-hit communities in rural Ontario aren't in it. Turning on the dashboard isn't enough — you'd need to expand the sites.