A Calgary-based family physician and urgent care doctor appeared on Canadian state media earlier this week to explain the alleged link between influenza, infection, and stroke.
When explaining the linkage, Dr. Raj Bhardwaj of the University of Calgary noted his recent surprise at discovering that there is now reportedly a “stroke season.”
What are the details?
Bhardwaj told CBC Calgary News that a stroke is ultimately when “the blood supply to the brain is compromised for some reason. It’s basically a plumbing problem in the pipes that supply blood to your brain. And there’s two things that could go wrong with pipes, right: they can get blocked or they can burst.”
Systemic inflammation resultant of influenza can reportedly help trigger these plumbing issues.
“It can make the inside of the pipes stickier. It can make your blood a little bit thicker, especially if you get dehydrated. And it can even put the heart into a weird rhythm called atrial fibrillation,” said Bhardwaj. “All of those things can increase your risk of having a stroke.”
While Bhardwaj was cognizant of the potential link between flu and stroke, he was nevertheless caught off guard by the alleged existence of a “stroke season.”
“I didn’t know about this either until last year, but it turns out that after flu season, about three or four weeks later, there is a stroke season,” he said. “Most of Canada is getting down off of a big hump of flu, so now we’re starting to see more strokes.”
Bhardwaj noted that he was not the only doctor in the dark about so-called “stroke season.”
“One of my colleagues actually mentioned that at work the other day and said, ‘Have you noticed how many strokes we’re seeing? It’s a lot more than usual it feels like,'” said Bhardwaj. “Anecdotally, we’re starting to see that.”
Bhardwaj claimed the “good news is that getting your flu shot reduces your risk of stroke,” citing a study from the University of Calgary where he works as a clinical assistant professor.
The study in question, published in the Lancet in November, noted that influenza “is a common respiratory infection that precedes stroke.”
Dr. Michael Hill, one of the authors on the study, told Global News, “There’s a longstanding history between infections and stroke — upper respiratory tract infections are associated with stroke — so it was sort of natural to start to look at this.”
The study suggested that after adjusting for demographics and comorbidities, “recent influenza vaccination significantly reduced the hazard of stroke”; an association that “persisted across all stroke types.”
Stroke was found to have been reduced across all ages and risk profiles with the exception to those without hypertension.
A spike resultant of lifestyle choices, weather or something else?
CTV News reported in December that one Canadian hospital had, like Bhardwaj’s colleague, observed a “15 per cent increase in the number of stroke patients arriving … in the first six months of this year.”
“What we’re seeing is that there is this measurable increase in in the risk of strokes, and not only that, but also just poor outcomes for patients that have strokes during the winter time,” said physician George Dresser.
Dresser suggested that regular exercise, reduced sodium and alcohol intake, and a potassium-rich diet could help remedy hypertension and, in turn, deter stroke.
Christmastime sloth and treats may not be the only triggers of spikes in stroke, however.
A 2016 study published in the Journal of Stroke and Cerebrovascular Diseases suggested that “lower average temperature and larger diurnal temperature variations were associated with stroke hospitalizations.”
Dr. Roberto Alejandro Cruz, a neurologist with DHR Health, told KRGV in May 2021 that he had noticed a spike in patients 30 years and older who had suffered strokes since the start of that year. The CDC noted that over 200 million COVID-19 vaccine doses had been administered in the United States by April 21.
While this particular study might help explain a wintertime or early spring “stroke season,” researchers behind a 2019 study published in the Journal of Stroke & Cerebrovascular Diseases suggested hot temperatures might otherwise trigger strokes.
They observed “an increase in [ischemic stroke] rates relative to [intracerebral hemorrhage] during the summer months with higher solar radiations that cannot be explained by physiological measures suggestive of dehydration or hem-concentration.”
Seasonal weather patterns might account for strokes, but not necessarily an significant uptick in cases.
The New York Times recently reported that data from the “Vaccine Safety Datalink, a federal safety surveillance system, hinted that Americans aged 65 and older might be at increased risk of an ischemic stroke in the 21 days after receiving” the bivalent booster shot.
The CDC — which the majority of respondents in a recent Rasmussen Report poll indicated they want investigated by Congress for its handling of vaccine safety — has announced that it is investigating whether the Bivalent Pfizer-BioNTech has increased some recipients’ risk of stroke. Despite the investigation, the CDC maintains that the risk posed by the booster is “very unlikely.”
Days after the CDC announced its investigation, Kate O’Brien, WHO director of Immunization, Vaccines and Biologicals, claimed that “the best evidence is that there is no true association between the booster doses of Pfizer in the older adults and strokes.”
A scientific review published June 2022 in the Journal of Stroke and Cerebrovascular Diseases noted that “Most of the evidence pertaining to stroke following COVID-19 vaccination are case reports, therefore, the incidence of stroke after COVID-19 vaccination is not precisely known.”
The review added that “Most patients who suffered from stroke after COVID-19 vaccination were women, under 60 years of age, and after the ChAdOx1 nCoV-19 vaccine.”
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