Almost 90 per cent of Ontario's growing measles cases are in the southwest

Measles case counts in Ontario continue to climb with the bulk of cases concentrated in southwestern Ontario, according to new data released by Public Health Ontario (PHO) on Thursday.

Health units that oversee that part of the province account for roughly 87.6 per cent of the cases recorded since the outbreak began this past fall. 

It's been traced to a Mennonite wedding in New Brunswick, Ontario's chief public health doctor said, and has since spread across the country. The result's been the largest measles outbreak Canada has seen in more than a decade. 

Public health officials in Ontario said they've now seen a total of 816 people with the measles, the majority in unvaccinated children.

The area around St. Thomas and Elgin county has seen the largest number of infections, with 32 new cases recorded this past week. Chatham-Kent also saw a spike with 47 new cases recorded in recent days.

 The regional numbers from October 28, 2024 to April 9 break down like this: 

• Southwestern Public Health: 238 (40.2 per cent).
• Grand Erie Public Health: 127 (15.6 per cent).
• Huron Perth Public Health: 94 (11.5 per cent).
• Chatham-Kent Public Health: 90 (11 per cent).
• South East Health: 58 (7.1 per cent).
• Windsor-Essex County Health: 44 (5.4 per cent).
• Region of Waterloo Public Health: 14 (1.7 per cent)
• Middlesex-London Health Unit: 12 (1.5 per cent)
• North Bay Parry Sound District: 11 (1.3 per cent).
• Grey Bruce Health Unit: 10 (1.2 per cent).
• Niagara Region Public Health: 10 (1.2 per cent)
• Wellington-Dufferin-Guelph: 9 (1.1 per cent)
• Lambton Public Health: 6 (0.7 per cent)
• Northeastern Public Health: 2 (0.2 per cent)
• City of Hamilton Public Health Services: 1 (0.1 per cent)

Across the province, 61 people have gone to hospital for treatment, three of which have resulted in ICU stays. No deaths have been reported.

Doctors urge vaccination

PHO's report also says 87.4 per cent of cases are in unvaccinated individuals, and another 9.7 per cent are in individuals with no proof of immunization, or whose immunization status is unknown.

"My message today is for parents and guardians in our region," said SWPH medical officer of health Dr. Ninh Tran during a media briefing Thursday. "If you have children attending school or childcare, it is important to know what to expect if there was a measles exposure in one of these settings." 

Health units are required to investigate possible exposures after receiving a positive measles test result, he said. While steps are taken to tell the public they may have been exposed, there's no guarantee the health unit can reach everyone. 

"The people who've had two doses of measles-containing vaccine are generally not at risk from that exposure as well," Tran added. "Those born before 1970 are generally not at risk. Under-immunized or unimmunized individuals are at risk from that exposure." 

Ontario’s measles outbreak prompts New York travel advisory

6 days ago

Duration 1:49

Measles cases are on the rise in Ontario and other parts of North America. The virus’s spread has become so large that public health officials in New York have issued a travel advisory to those travelling to Ontario. CBC’s Greg Ross has the latest on what people need to know.

A memo from Ontario's chief medical officer of health Dr. Kieran Moore in March confirmed that the current outbreak was from a "large gathering with guests from Mennonite communities in New Brunswick last fall."

Most people in the province still track their shots on paper, which the Ontario Immunization Advisory Committee is encouraging the Ministry of Health to change. 

"[A digital registry] would save a lot of additional time and energy for parents, for healthcare providers and as far as ourselves and it would really help guide our response. That would be incredible," Tran said.