(Toronto) Whooping cough is on track to hit a record number of cases in Ontario as infections rise in eastern provinces and decline in Quebec, but experts say it has been particularly difficult this year to predict how the highly contagious disease will evolve.
This is the first time the disease has circulated significantly since the pre-pandemic years and, unlike influenza, it does not follow a predictable pattern, other than a resurgence every two or three years, says Dr.r Jesse Papenburg, a pediatric infectious disease specialist at the McGill University Health Centre.
As with other respiratory diseases, Dr Papenburg says we’re still learning how public health measures put in place during the pandemic have disrupted the typical cycle of whooping cough outbreaks.
Provincial figures show the vaccine-preventable disease, also known as the “100-day cough,” has surpassed pre-pandemic record numbers in Quebec, Ontario, New Brunswick, Prince Edward Island and Newfoundland and Labrador. Western provinces are seeing normal numbers.
The rates are particularly high in Ontario, where public health data released Wednesday included one adult death but no details on the case.
The disease is most dangerous for unvaccinated infants, children and the elderly, according to infectious disease physician Dr.r Isaac Bogoch.
He nevertheless recalled that adult deaths were rare.
“I can’t remember the last time I heard of a fatal case in an adult in Canada, but certainly if we look at the literature, we know it does happen,” said Dr.r Bogoch.
“We certainly know that there are underlying medical conditions that increase the risk of serious illness and, unfortunately, mortality can occur at any age.”
Explosions of cases in the provinces
Ontario is on track to surpass its highest case count since 2012, when 1,044 cases were reported, according to Public Health Ontario. There were 1,016 cases in Ontario as of Sept. 9. That compares to 470 cases last reported in June and the five-year average to date of 98, according to a provincial dashboard.
“A lot of infections are in the younger cohort. They haven’t completed a full series of vaccinations and they may have some protection, but not as much as they could have and they’re still susceptible,” says Dr.r Bogoch.
Even among vaccinated people, immune protection is relatively short-lived, lasting only a few years, Dr.r Papenburg.
In Quebec, where cases are the highest in the country with 13,716 cases reported so far this year, he suggests the surge could actually dampen the spread during the back-to-school period.
Since we’ve already had a lot of cases, there are a lot of people who have developed more and more natural immunity in the community. We’re obviously still in an epidemic period. We’re still detecting a lot of cases, but the number of cases per week seems to be decreasing.
Dr Jesse Papenburg, a pediatric infectious disease specialist at the McGill University Health Centre
Public health officials also say the number of weekly cases has been declining over the past month, but Quebec Health Ministry spokesperson Marie-Claude Lacasse says “it’s too early to say whether this will continue or whether the return to school will lead to an increase in new infections.”
The experts, including Le Dr Bogoch, stress that vaccination is a key measure to contain outbreaks. Newfoundland and Labrador Health Services has expanded its pertussis vaccination program this school year to offer booster doses to students in grades 8 and 10.e year, in addition to those of 9e year. The Atlantic province recorded 236 cases of whooping cough, compared to an average of six per year before the pandemic.
New Brunswick health officials are reporting 286 infections as of Wednesday, which is “significantly higher” than the five-year average of 35 before the pandemic.
Prince Edward Island, which typically sees zero to three cases a year, has reported 41 cases, a quarter of which were recorded in the past two weeks alone.
The importance of vaccination
“There are probably many different reasons why we are seeing this increase in cases, but we have levers that we can pull and we have some things that we can control. The simplest one is vaccination,” says Dr.r Isaac Bogoch.
Routine vaccines that protect children against whooping cough are scheduled at two months, four months, and six months, followed by a booster at 18 months and later in childhood and adolescence. The vaccine is also recommended for adults and during pregnancy.
In western British Columbia, 122 cases have been recorded this year, which health officials say is at “historic levels,” while Alberta has recorded 445, compared to a five-year pre-pandemic average of 527. Nunavut, meanwhile, declared the outbreak over in August.
Looking at the overall situation across the country, Dr Bogoch says it’s a little early to say whether cases are increasing or decreasing. “We would need to see a significant trend over time in multiple geographic contexts before we draw conclusions from that,” he says.
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