After adding only one case last week, Region of Waterloo Public Health is now reporting 21 additional cases of measles in the municipality.
This comes as the provincial health agency is reporting 96 new measles cases in the province over the past week, bringing the total number to 2,179 since an outbreak began in October.
According to a Region of Waterloo spokesperson, the province recently changed definitions for outbreaks meaning it altered the case count over the last week.
“As the list of criteria required to link cases to the outbreak has expanded, historical cases (from May 2025) that did not previously meet the case definition have now been included in Public Health Ontario’s weekly measles summary,” Gloria Bairos told CityNews. “As a result, the total number of cases in the Region of Waterloo as reported by the province has increased even though there have been no new cases reported in the past week.”
Last week, Foundation Christian School on Katherine Street in West Montrose was added to the Region of Waterloo’s list of potential public exposures to measles, one of several schools that have had measles cases.
A northern Ontario region that saw its first measles infection in April is now seeing dozens of new cases for the third week in a row.
Thirty-four of the new infections are in Algoma Public Health, which includes Sault Ste. Marie. Last week, it had 28 new infections, which have been rising since April 23 when it reported its first case this year.
That raises the northern health unit’s count to 115 and includes three hospitalizations.
Dr. John Tuinema, Algoma’s associate medical officer of health, says this uptick was expected.
“Our first case happened a couple months after a lot of what happened in Southwestern Ontario, so I would say that we are in a similar place that they would have been a few months prior,” says Tuinema.
But Tuinema says his northern region likely won’t reach the number seen in southwestern Ontario because of a high vaccination rate and small population size.
According to Algoma Public Health, 87 per cent of seven-year-olds and 97 per cent of 17-year-olds are vaccinated against measles.
“When we do have a case, if they do have contact with people who are immunized, that kind of quickly hits that wall of herd immunity. But it’s still sort of working its way through some of the unimmunized population. It’s almost exclusively been in private settings, such as households,” says Tuinema.
Southwestern Public Health, considered the provincial hotspot of the outbreak over the last seven months, has recorded a total of 751 cases.
That includes 12 new infections, which have been decreasing week by week over the last month.