Whooping cough is surging in several parts of Canada, most notably in Quebec, where more than 12,000 people have caught the bacterial illness since the start of the year.
Most of the 12,388 cases that the Quebec Health Ministry reported as of Saturday are part of a summer spike that far outstrips the norm in prepandemic years, when an average of just under 600 cases of whooping cough were reported in the first eight months of the year between 2015 and 2019.
Many of the cases in Quebec and elsewhere have been diagnosed in school-age children, prompting public-health officials to urge parents to ensure students have received all their recommended vaccines before heading back to school.
“Make no mistake, there is an epidemic in Quebec,” said Jesse Papenburg, an infectious disease physician and medical microbiologist at Montreal Children’s Hospital. “But on the other hand, it’s normal to have an epidemic every three to five years. That is the expected cyclical pattern that we see with whooping cough.”
Still, Dr. Papenburg and other infectious disease experts said the normal cyclical pattern of whooping cough outbreaks may have been disrupted by the COVID-19 pandemic and the public-health measures imposed to control it.
Canada and many of the other countries experiencing increases in whooping cough this year were likely overdue for major outbreaks, they said. Dr. Papenburg said the testing infrastructure built for COVID is also used for other illnesses and may be picking up more cases of whooping cough.
The World Health Organization issued a whooping cough alert for the Americas region last month, a few months after the European Centre for Disease Prevention and Control warned in May of a substantial increase in cases on the continent.
Whooping cough, also known as pertussis, spreads through respiratory droplets and close contact. It is sometimes referred to as the 100-day cough because of the staying power of the symptoms, which include a telltale bark that can leave sufferers short of breath.
The vast majority of people who catch whooping cough recover without needing to go to hospital, but the illness can, in rare cases, be fatal in infants. None of the provincial or territorial health authorities that responded to The Globe and Mail’s queries noted any deaths attributed to whooping cough this year, including Quebec. Quebec’s Health Ministry said by e-mail that 0.7 per cent of cases required hospital admission, most children under 5.
New Brunswick, which has recorded 141 cases so far this year, last week declared a provincewide outbreak of whooping cough. The province normally records just more than 30 cases in a full year. Prince Edward Island also declared an outbreak in August, while Newfoundland and Labrador reported an outbreak on the eastern side of the island in May. Nova Scotia has recorded only nine cases acquired in the community, low compared to its neighbours.
Ontario is seeing a rise in whooping cough, though not to the same degree as in Quebec. The most recent infectious diseases surveillance report from Public Health Ontario notes 470 cases of pertussis as of the end of June, up from an average of 98 cases in the first six months of the last five years.
While cycles of whooping cough can’t necessarily be predicted from one year to the next, “they do reliably occur over time in response to several factors, like waning population immunity, vaccination coverage in the population, or even small changes in the bacteria itself,” said Reed Morrison, a public-health physician with Public Health Ontario. “So, this year, it’s very likely that all of these factors are working together and contributing to the rise in pertussis activity.”
The trends in Western Canada don’t mirror those in the east. The British Columbia Centre for Disease Control, for example, has recorded 101 cases of pertussis as of Tuesday, lower than any other year of the past decade except for 2021, 2022 and 2023, when pandemic-control measures suppressed respiratory illnesses. Alberta has reported 399 cases, which a spokesman for Alberta Health Services said was consistent with the typical annual case count, which usually ranges in the few hundreds.
Manitoba has reported 97 cases so far this year, down from 334 last year, when an outbreak occurred in a part of southern Manitoba with low immunization rates. Saskatchewan, however, reported 34 cases as of the end of July, an increase from 13 in the same period last year. Yukon, which didn’t report a case in the previous five years, has recorded six so far this year. The Northwest Territories has had no recorded cases this year, and Nunavut did not respond to The Globe’s query.
The whooping cough vaccine is generally given as part of a routine vaccination schedule at two months, four months, six months and 18 months of age, followed by a booster dose around the time children start school and another shot in their early teens.
One booster dose is also recommended for all adults over the age of 18 and for women during pregnancy, when the shot provides antibodies to vulnerable newborns.
“Anyone who’s not up to date on their vaccines can get whooping cough,” said Yves Léger, the acting chief medical officer of health for New Brunswick. But he emphasized that infants, especially those too young to have received their first doses of the vaccine, are most at risk. “They’re really the ones that we want to make sure that we protect, because they’re the ones that are at risk of complications like pneumonia, swelling of the brain, hospitalization and even death.”