Measles ‘inevitable’ in Ottawa, expert warns as outbreak spreads

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Ottawa Public Health has begun monitoring wastewater for evidence of measles in the city as the highly infectious disease continues to surge throughout Ontario.

That makes Ottawa one of the only communities in the province and across Canada using wastewater as a possible early warning signal for measles. Ottawa Public Health says the tool is promising for detecting measles, but the research is limited and “many unknowns remain”.

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There have been no cases in Ottawa so far this year but Dr. Gregory Rose, who is director of infection prevention and control at Queensway Carleton Hospital, warns that it is only a matter of time.

“It is inevitable we will have cases in Ottawa,” said Rose, noting the size of the ongoing outbreak in the province. “The likelihood is that we will definitely see exposed people and quite possibly infected people in the very near future. In my years, we have not had this kind of burden of disease in the province.” Queensway Carleton, he said, is geared up to watch for potential cases and isolate patients.

There had been 440 cases in the province so far this year, mainly in unvaccinated children, in the last update from Public Health Ontario almost a week ago. That number has almost certainly increased since then. It is the largest outbreak in the province since measles was considered eliminated in Canada in 1998 due to successful vaccination programs. Most of those cases have been centred in southwestern Ontario, but measles cases have also been reported across a broader swath of the province, including in parts of Eastern Ontario. Ottawa’s last reported measles case was in 2019.

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Ottawa has been a leader in wastewater testing, pioneering it early in the pandemic to monitor COVID-19 levels. It is one of the only communities in the province that maintained a wastewater testing program after the province cancelled funding last year. Ottawa Public Health regularly monitors testing results for influenza, RSV and COVID-19.

Earlier this year, as the measles outbreak expanded in Ontario, public health officials also began getting regular reports of wastewater testing for the virus that causes measles, said Robert Delatolla, the uOttawa researcher who has led the wastewater surveillance program in the city that is now supported by OPH and CHEO in addition to research funding.

Delatolla said his lab has been doing measles testing for research purposes since late 2023 and has gone back to test earlier samples as well. Several times, the test indicated weak signals of the measles virus in wastewater, but subsequent testing indicated that was as a result of people getting vaccinated. The vaccine contains a weakened form of the virus. It is designed to trigger an immune response but is not strong enough to cause the disease. It also has a different genetic makeup than the wild virus that is infecting people in Ontario.

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Delatolla said that tells researchers that the test is highly sensitive and should be able to pick up measles in the city’s wastewater with a small number of infections, something that could give public health officials a heads up to prevent broad spread.

His lab is currently testing for measles three times a week and reporting to Ottawa Public Health weekly. So far, there has been no evidence of the virus in wastewater.

Dr. Michelle Foote, associate medical officer of health at OPH, noted that wastewater testing has yet to be “validated” in Ottawa to see how well it detects the strain of measles currently circulating in Ontario. But if wastewater surveillance proves effective at detecting the wild virus circulating in Ontario “detection would reiterate the importance of prevention measures, including ensuring that one’s measles vaccines are up to date.”

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Delatolla said he has worked with a researcher in the Windsor area, where there have been measles cases, who is also doing wastewater testing there. There is no government-funded wastewater testing for measles in Ontario, nor is the Public Health Agency of Canada undertaking any.

Delatolla said he has heard from other researchers and health officials who have said they wish they still had access to wastewater surveillance data to track measles.

He said the goal of wastewater testing is to prevent the spread of infectious diseases by having an early warning signal to take public health measures. He said wastewater surveillance should be able to help pinpoint parts of the city, or even buildings, where an infection is present.

Queensway Carleton Hospital infectious disease specialist Rose, meanwhile, said QCH is screening for patients in the emergency department who could potentially have measles, but has not had any positive cases. Testing required to confirm measles has to be sent to Toronto, and results can take several days.

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He noted that one in five patients with measles has to be admitted to hospital. One in 20 patients will develop measles pneumonia, one out of 1,000 children who are infected will develop encephalitis, and the death rate from measles is about one in 1,000. Measles can also eliminate immunity to other illnesses. And one infected person can spread measles to up to 18 people who are vulnerable.

Rose said it is frustrating to see the return of a serious and potentially deadly disease that can be prevented by a highly effective and safe vaccine.

His message to members of the public is: “If there is any doubt about your vaccination status, get vaccinated.”

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