Whooping cough is on track to hit a record number of cases in Ontario, while infections are rising in the eastern provinces and declining in Quebec, but experts say it has been particularly difficult this year to predict the evolution of the highly contagious disease.
This is the first time the disease has spread significantly since the pre-pandemic years, and unlike influenza, it doesn't follow a predictable pattern, other than reappearing every two or three years, explains Dr. Jesse Babenberg, a pediatric infectious disease specialist at McGill University Health Centre.
As with other respiratory diseases, Dr. Papenburg says we are still learning how public health measures taken during the pandemic have disrupted the typical cycle of whooping cough outbreaks.
Regional figures show that the vaccine-preventable disease, also calledcough for 100 days“Pre-pandemic records were surpassed in Quebec, Ontario, New Brunswick, Prince Edward Island and Newfoundland and Labrador. Western provinces reported normal numbers.
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 older adults, according to infectious disease physician Dr. Isaac Bogoch.
However, he noted 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 that it does happen.“Dr. Bogoch explained,”
“We certainly know that there are underlying medical conditions that increase the risk of serious illness, and unfortunately, deaths can occur at any age.”
Cases explode in the provinces
Ontario is on track to surpass the highest number of cases 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 the provincial dashboard.
“Many infections affect the younger group. They have not completed the full series of vaccinations and may have some protection, but not as much as they could have and they are still vulnerable to infection.“,” explains Dr. Bogoch.
Even among people who are vaccinated, immune protection is relatively short-lived, lasting only a few years, Dr. Papenburg says.
In Quebec, where cases are the highest in the country with 13,716 reported so far this year, that suggests the increase could actually reduce the spread of the disease during the back-to-school period.”Because we already had so many cases, there are a lot of people who have developed more and more natural immunity in the community.The doctor explains before adding:We are clearly still in the pandemic. We are still finding a lot of cases, but the number of cases per week seems to be decreasing.»
Public health officials also say the number of weekly cases has declined over the past month, but Quebec health ministry spokeswoman Marie-Claude Lacasse says,It is too early to say whether this will continue or whether the start of the school year will lead to an increase in new infections.“
Experts, including Dr. Bogoch, stress that vaccination is key to containing the outbreak. Newfoundland and Labrador Health Services expanded its pertussis vaccination program this school year to offer booster shots to Grade 8 students, as well as Grade 9 students. The Atlantic province has recorded 236 cases of pertussis, compared to an average of six cases per year before the pandemic.
New Brunswick health officials reported 286 new cases on Wednesday, amuch higher» 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 have been recorded in just the past two weeks.
The importance of vaccination
“There are probably many different reasons why we're seeing this increase in cases, but we have some levers that we can pull and we have some things that we can control. The simplest is vaccination.“Dr. Isaac Bogush explains,”
Routine vaccinations that protect children against pertussis are scheduled at 2 months, 4 months, and 6 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, there have been 122 cases this year, which health officials say is within “historical levels,” while Alberta has recorded 445 cases, compared with the five-year pre-pandemic average of 527. The pandemic was declared over in August.
Given the overall situation across the country, Dr. Bogoch says it’s a bit early to tell whether cases are increasing or decreasing. “We’ll need to see a significant trend over time in many geographic contexts before we can draw any conclusions from that,” he says.
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Hannah Alberga, The Canadian Press
