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Infectious Diseases

13 July 2020

Stroke appears 8 times more likely with Covid than with flu

Covid-19 disease has been associated with blood clots that could increase stroke risk.

  • Research supports the notion that Covid-19 is more severe than regular influenza
  • The risk for stroke is many times higher in Covid-19 patients than in patients with flu
  • Covid-19 attacks the cells that line blood vessels, increasing the risk for blood clots that can lead to stroke


Both flu and Covid-19 can raise your risk for a stroke, but the odds appear to be eight times higher with the coronavirus, a new study finds.

Among more than 1 900 patients with Covid-19, 1.6% suffered a stroke, versus 0.2% of nearly 1 500 patients seriously ill with flu, researchers found.

"Doctors and practitioners taking care of patients with Covid-19 infection should remain vigilant for signs and symptoms of stroke, because prompt diagnosis may permit effective stroke treatment," said researcher Dr Neal Parikh, an assistant professor of neurology and neuroscience at Weill Cornell Medicine in New York City.

"Fundamentally, our results support the notion that Covid-19 infection is more severe than influenza infection," Parikh added.

Complication of infection

For the study, Parikh and colleagues compared the incidence of stroke among Covid patients and flu patients in two New York City hospitals. Patients with coronavirus were assessed from 4 March through 2 May, while researchers analysed flu data from 1 January 2016, through 31 May 2018.

Two neurologists who reviewed the findings weren't surprised that Covid was linked with stroke.

"Infections and other inflammatory conditions are established risk factors for stroke, so it is not surprising that patients with Covid-19 disease might have stroke as a complication of the infection," said Dr Larry Goldstein, professor and chairman of neurology at the University of Kentucky.

Covid-19 disease has also been associated with blood clots that could increase stroke risk, he said.

Dr Salman Azhar is director of stroke at Lenox Hill Hospital in New York City. He said, "This virus has a predilection to cause some level of clotting, and we think that maybe it's because of increases in inflammation in the body."

Trying to prevent clots

Azhar explained that Covid-19 attacks the cells that line blood vessels, which is one reason for the increased risk for blood clots leading to stroke. Also, the virus increases the production of clotting factors, he said.

Antibodies also play a role in the development of stroke, Azhar said.

"There are antibodies that we've known for a long time, nothing to do with this virus, but we know increase people's risk to have strokes and other blood vessel clots, and we are seeing them in a higher incidence in patients with Covid-19," Azhar said.

Because of these risks, Covid-19 patients are monitored for signs of clotting. In general, "every patient with Covid-19 gets put on low-level blood thinners to try and prevent clots," Azhar said.

"Patients who have clots are put on higher doses of blood thinners to keep them from having clots that may damage vital organs," he said.

Both young and old Covid patients can develop clots, with the sickest most at risk, Azhar said.

Propensity for blood clot formation

In some patients, stroke may be the first sign of Covid-19. In this study, more than one-quarter of patients went to the emergency room because of a stroke and were later diagnosed with the coronavirus.

Fortunately, only a small percentage of Covid-19 patients have strokes, Azhar said. Out of 1 916 patients who had the virus in the study, 31 suffered a stroke. However, the disability after a stroke can be a lasting effect of the virus, he said.

Not all parts of the country have seen the same risk of stroke in Covid patients as reported in New York, said Goldstein, whose practice is in Lexington, Kentucky.

"We have yet to have a single patient with both conditions, although the number with Covid-19 in our area is thankfully much lower than in New York," he noted. "Regardless, Covid-19 disease is clearly associated with a propensity for blood clot formation, and stroke needs to be considered as a possible complication."

The report was published online on 2 July in the journal JAMA Neurology.

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