Ontario measles outbreak grows to more than 800 cases

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Health officials have reported 155 new measles cases in Ontario during the past week alone, as the outbreak that began last October continues to grow.

So far, 816 cases of the highly infectious disease have been associated with the outbreak, which health officials say began with a Mennonite community gathering in New Brunswick last fall. The outbreak in New Brunswick was declared over in January, but Ontario’s has continued to spread. It is the largest outbreak in the province since measles was considered eliminated in Canada in the 1990s.

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Cases were originally centred around two health units in southwestern Ontario, but have now spread throughout the province, to 15 health units. There have been no cases in Ottawa, which is one of the only communities in the province that uses wastewater testing as a surveillance and early warning tool for measles. There have been 58 cases in the South East Health Unit, which includes Belleville, Kingston and surrounding areas. Southwestern Public Health, which includes Oxford County, Elgin County and St. Thomas, is the epicentre of the outbreak. So far it has had 328 measles cases, 40 per cent of the provincial total.

The majority of cases have been among infants, children and adolescents, most of them unvaccinated. Sixty-one cases associated with the outbreak have required hospitalization, six of them in intensive care. There have been no deaths associated with the outbreak.

There have been an additional 25 cases in Ontario since January that were not linked to the multi-jurisdictional outbreak. Some are connected with travel. In other cases no source has been identified.

Waning vaccination coverage since the pandemic has allowed the outbreak to grow and spread. A shortage of primary caregivers, missed appointments during the pandemic and increasing misinformation about vaccines have all contributed to lower vaccination rates, especially in pockets of some communities.

Compared to the 816 Ontario cases associated with the outbreak in less than six months, there were 101 confirmed cases over a period of 10 years in the province between 2013 and 2023.

This week’s surge in cases is higher than a week ago, meaning that the outbreak, which appeared to be losing steam, is still growing.

Measles is so infectious that one person can infect up to 18 susceptible people. Symptoms include fever, cough, runny nose and red, watery eyes followed by a red, blotchy rash that appears on the face and spreads.

Measles can cause ear infections, pneumonia, encephalitis and even death.

New York State recently issued a travel advisory based on Ontario’s measles outbreak.

For more information on measles: cheo.on.ca/en/resources-and-support/measles.aspx