TORONTO -- According to a new study, for some COVID-19 patients, the very first sign of the virus attacking their system doesn’t come in the form of a cough or difficulty breathing but in something far deadlier: a stroke.

Scientists are learning more about the effects of COVID-19 on the body, and one of the more troubling and long-lasting concerns is a link to strokes.

A study published in the scientific journal Neurology on Tuesday collected data on 160 stroke patients with COVID-19, 29 of whom were under the age of 50.

When it came to these younger patients, 45 per cent had no risk factors for COVID-19, and in 50 per cent of the cases involving younger patients, suffering a stroke was their first symptom of COVID-19.

This means that half of the younger COVID-19 patients in the study displayed zero COVID-19 symptoms before the onset of a stroke.

“They’re totally healthy people who develop COVID-19 and they've got strokes,” Dr. Luciano Sposato, one of the researchers from Western University, told CTV News. “That was quite surprising.”

The study is an alert to doctors and patients that during this pandemic, sometimes a stroke is more than it appears.

“When we see patients with stroke, the first thing that we need to keep in mind is that they are at very high risk of having COVID-19,” Sposato said. Even in the absence of symptoms, they should be tested, he added, because stroke patients with COVID-19 are at a far higher risk of death when compared to stroke patients without COVID-19.

Up to 45 per cent of stroke patients in the ICU with COVID-19 don't survive, the study revealed, compared to the 15 to 30 per cent mortality rate of stroke patients without COVID-19 in the ICU.

When researchers looked at other factors, the death rate rose even higher.

The highest risk group in the study were those who had at least one significant comorbidity (meaning they also had another risk factor such as obesity, hypertension, diabetes, etc.) as well as severe COVID-19 symptoms.

Stroke patients in this group had a mortality rate of 59 per cent.

Compared to similar respiratory illnesses, COVID-19’s link to strokes was much stronger.

COVID-19 patients are ten times more likely than influenza patients to suffer a stroke, and more than twice as likely as SARS patients, according to the study.

Scientists believe that strokes linked to COVID-19 are different than the regular kind.

In these cases, scientists think the virus enters some cells that line the blood vessels, triggering inflammation and potentially causing blood clots to form in the lungs, the legs or the heart.

“There's something interesting about other comorbidities that these patients have, for example, if you look at clots in the pulmonary arteries, [they] are 14 times more frequent in patients with stroke and COVID-19 than with patients with stroke and no signs of COVID-19, based on historical data from Canada,” Sposato said.

These clots can even move to the brain. This causes an ischemic stroke, where an artery blockage cuts off blood flow to the brain.

In this study, the number of patients who developed large clots in the arteries that specifically supply blood to the brain was much higher than previous studies of ischemic stroke patients who did not have COVID-19, with 49 per cent developing large clots versus 29 per cent in patients without COVID-19.

Surviving a stroke can have long-lasting impacts on the body as well. Those who make it through can be left with problems speaking or walking.

“Stroke is the leading cause of major disability in North America, and anything that can increase the likelihood of having strokes, particularly in a younger population, [is] a public health priority and needs immediate attention,” Dr. Luciana Catanese, physician lead for hyperacute stroke services at Hamilton Health Sciences, told CTV News.

Standard stroke treatment and blood thinners appear to help these patients. But fast medical attention is critical.

The warning signs for a stroke are sudden numbness, confusion, trouble speaking, vision loss and trouble walking.

“If you would experience any stroke symptoms, [please] feel safe to call 911, and to come to the hospital, because we have everything in place to provide safe and protected care during the COVID pandemic,” Dr. Aleksandra Pikula, a stroke neurologist with the Toronto Western Hospital, told CTV News.

The findings underline the extensive reach of COVID-19 within the body, and how it can impact other parts of a person’s health, with sometimes long-lasting consequences.

“We're not done with this disease and we're starting to see problems, not only in the lungs, but also in the brain and heart,” Sposato said. 

In order to better understand the connection between strokes and COVID-19, Pikula and Catanese are co-leading a national study into the link.

The study will “be looking into the stroke complications of COVID,” Pikula said.

“We want to ultimately be able to understand this association and be able to understand, with a larger number of patients, what kind of patients do have strokes, what kind of strokes, and what are the ultimate causes of the stroke, so […] we’re better positioned to treat these strokes and improve the outcome of these patients,” Catanese added.