Ontario saw the highest number of whooping cough cases in the last 17 years: report

An infant receives a routine vaccination at First Georgia Physician Group Pediatrics in Fayetteville, Ga., Tuesday, Aug. 17, 2021. (Angie Wang / The Canadian Press / AP)

The number of whooping cough cases in Ontario this year has reached a level that hasn’t been seen in 17 years.

In November, Public Health Ontario (PHO) published its findings on pertussis, commonly known as whooping cough, delving into its activity by exploring case characteristics, counts and incidence rates.

Pertussis is a bacterial infection that attacks your respiratory tract with infections leading to chronic coughing, potentially bringing on symptoms like burst blood vessels or even broken ribs in children. It's typically seen as a cough with a high-pitched whoop at the end, Dr. Allan Grill, chief of family medicine at Markham Stouffville Hospital, told CTV News Toronto.

"A lot of people described episodes of coughing, so much so that at the end they have vomiting," Grill explained in an interview Friday.

It's the type of infection that needs to get diagnosed relatively quickly when symptoms start, he added.

"The earlier we treat the pertussis, the better," Grill said. "If a young infant is having breath-holding spells or looks like they have trouble breathing, you can't mess around. You have to seek care immediately because that population can get very sick from pertussis."

As of the date of publication, on Nov. 7, the provincial health agency says there have been a total of 1,475 cases – confirmed and probable – seen in Ontario this year, with a rate of around nine cases for every 100,000 people. Both the case count and rate are the highest the PHO has observed since 2007.

For Toronto alone, Toronto Public Health confirmed to CTV News Toronto that there has been a "notable" rise in whooping cough cases in the city, with 187 confirmed cases as of Nov. 30. For the same period, TPH noted the pre-pandemic average is 31 cases.

Based on TPH's numbers, the amount of cases in 2024 roughly octupled compared to last year, which saw 22 confirmed cases.

The report notes cases started rising between March and October, with cases peaking in July.

"I think it's always a concern when you have more cases because you start to think who's at risk of the most severe disease," Grill said, though noted he and his colleagues haven't seen as many whooping cough cases as of late.

Weeks-old infants and children between the ages of 10 and 14 have the highest number of cases, with an incidence rate of 69 and roughly 50 cases for every 100,000 children, respectively – a rate the report notes far exceeds the five-year pre-pandemic average.

The PHO said 41 of the 58 reported hospitalizations saw children under the age of 18 admitted, with just over 70 per cent, or 29 cases, involving kids between two to 51 weeks old. Four infants were also admitted to the intensive care unit, the report noted.

"We definitely worry about that population, and then you start to think, 'Well, why are we seeing so many cases?'" Grill said, pointing to the report's findings that a quarter of people who contracted the infection this year were not immunized for it.

"I think the key message as a family doctor when you hear about an uptick in pertussis is, 'How are we doing with vaccinations?' And I would remind my patients and the public that we have a publicly-funded immunization program in Ontario, and specifically for whooping cough."

A series of four vaccines are publicly offered to children between two and 18 months old, the PHO said in its report, with booster doses provided to kids again at four, 14 and 24 years of age. Grill also pointed to another immunization program offered to those who are pregnant, when they are about 27 to 32 weeks along in their pregnancy.

While the booster vaccines won't completely eliminate the contraction of whooping cough, Grill said it does significantly decrease the spread from person to person, as pertussis is usually passed on by a cough or sneeze.

PHO noted that nearly 40 per cent of pertussis cases this year were immunized with at least one dose, but Grill said it was crucial to complete the series of doses.

"I always say to people, 'Unimmunized is not good, but under-immunized isn't great either' because the whole reason we have a publicly-funded immunization schedule is because it's based on good scientific evidence," Grill said.

Pertussis activity is cyclical, the PHO noted, with occasional increases seen every two to six years. The provincial health agency revealed Ontario had seen the lowest number of recorded cases at the height of the pandemic.

Grill said while the number of cases peaked in July, cases have been dwindling since then, adding that he and his colleagues in the emergency department have not been seeing a ton of active cases lately.

With files from CTV News' Senior Correspondent Adrian Ghobrial