Whooping cough cases are soaring to new heights in Canada. What's behind the sudden spike?

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The classic sound of whooping cough is grating and unmistakable: A harsh, deep hacking that's often followed by a distinctive "whoop" as patients struggle to breathe.

It's not the kind of infection anyone wants to get, and for vulnerable individuals, it can turn deadly. But the number of people catching it recently in Canada — kids and teens, primarily — is soaring to staggering levels.

More than 12,000 cases of whooping cough, also known as pertussis or the 100-day cough, have been reported to date in 2024, the Public Health Agency of Canada (PHAC) told CBC News, citing media reports from across the country. That's far higher than the roughly 500 to 4,500 nationwide infections typically reported each year. 

Caused by a bacteria called Bordetella pertussis, the vast majority of this year's whooping cough cases are in Quebec, though various other provinces also started experiencing outbreaks or higher-than-usual case counts in recent months. So far, the disease is mainly striking youth aged 10 to 14, Quebec health officials recently told The Canadian Press. 

"Although increased pertussis activity is expected after record-low activity during the pandemic years … the numbers of cases seen in Quebec, New Brunswick, Prince Edward Island and Newfoundland and Labrador in 2024 exceed pre-pandemic peak years," a PHAC spokesperson said in a statement. 

The massive spike in infections echoes a similar trend seen in the U.S. and across Europe over the last year. And scientists familiar with whooping cough say the surge is caused by a confluence of factors, creating a perfect storm that's putting society's youngest at risk of serious illness.

"I think what happened is not a surprise given the cyclical nature of how we see pertussis, but what's a surprise is the magnitude and the scale," said clinician-scientist Dr. May ElSherif, the associate director for laboratory management at the Canadian Centre for Vaccinology in Halifax.

Pertussis is highly contagious, and while symptoms can be mild for many individuals, infections can also lead to pneumonia, brain damage or life-threatening illness. 

"Whooping cough isn't just something that's kind of in Victorian novels. It's something that people still get and it can be very disabling," said infectious diseases specialist Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security in Baltimore.

"Adults often break their ribs because they cough so violently."

But newborns, particularly those who don't yet have any protection from pertussis vaccines, are also among those getting the sickest or even dying, stressed Dr. Jesse Papenburg, a clinician and researcher with the Montreal Children's Hospital.

"It's really children — young children, infants, and especially those around six months of life — that are at highest risk of complications," he said.

During Europe's recent pertussis outbreak, which involved more than 60,000 total cases throughout 2023 and the first quarter of 2024, at least eight older adults died along with 11 infants, according to the European Centre for Disease Prevention and Control.