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Risk of stroke is almost eight times higher for COVID-19 patients than for flu patients, study finds

All the strokes in the study were ischemic, the most common kind. An ischemic stroke occurs when a blood clot blocks a blood vessel to the brain.

coronavirus patient
REUTERS/Lucy Nicholson
After adjusting for other factors associated with an increased risk of stroke, such as age, gender and race, the researchers calculated that the likelihood of stroke was 7.6 times higher for people with a COVID-19 infection than for those with influenza.
People with COVID-19 are almost eight times more likely to experience a stroke during their illness than people with influenza, according to a study published late last week in JAMA Neurology.

This finding suggests that doctors should be alert for symptoms and signs of stroke in people with COVID-19 so that the patients can receive prompt treatment, if possible, to reduce the risk of stroke-related long-term disabilities, such as loss of control over body movements and aphasia (difficulty speaking), say the study’s authors.

The finding also underscores how much more serious COVID-19 is than the seasonal flu.

“Although the overall rate of stroke in patients with COVID-19 was low, the rate was substantially higher than among patients with influenza,” said Dr. Neal Parikh, one of the study’s authors and a neurologist at Cornell University, in an interview with MedPage Today reporter Judy George.

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“Fundamentally, our results support the notion that COVID-19 infection is more severe than influenza infection,” he added.

Study details

This isn’t the first study to link COVID-19 with an increased risk of stroke. But previous reports of such a connection lacked appropriate control groups. The current study is designed to overcome that problem.

For the study, Parikh and his colleagues compared data collected from two groups of patients treated at two New York City hospitals. One group consisted of 1,916 patients with test-confirmed cases of COVID-19 who received emergency department care or were hospitalized between March 4 and May 2, 2020. The other group — the “control” — included 1,916 patients with test-confirmed influenza who were hospitalized between January 2016 and May 2018.

Among the COVID-19 patients, 31 (1.6 percent) experienced a stroke. By comparison, three of the influenza patients (0.2 percent) had a stroke. After adjusting for other factors associated with an increased risk of stroke, such as age, gender and race, the researchers calculated that the likelihood of stroke was 7.6 times higher for people with a COVID-19 infection than for those with influenza.

All the strokes in the study were ischemic, the most common kind. An ischemic stroke occurs when a blood clot blocks a blood vessel to the brain. (The other type of stroke, hemorrhagic, occurs when a weakened blood vessel in the brain ruptures.)

The ages of the COVID-19 patients who had a stroke ranged from 66 to 78. The length of time between the onset of their COVID-19 symptoms and their stroke varied from five to 28 days. More than a third of them had severe cases of COVID-19 and had received mechanical ventilation.

Limitations and implications

This research comes with caveats. To begin with, as Parikh and his colleagues point out, the study may have underestimated the true rate of stroke in patients hospitalized with COVID-19 because some of those patients may have been too unstable to undergo brain imaging (needed for a diagnosis of stroke), or they may have died before reaching the hospital. On the other hand, the study may have overestimated the stroke rate in people with COVID-19 because infected patients who were admitted to New York hospitals during March and April, a period when cases were surging in that city, may have been more severely ill than patients who were hospitalized for influenza in recent years.

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In addition, the study involved only patients at two hospitals in one city. The findings may not be generalizable to patients in other locations.

Still, there are good reasons people with COVID-19 may be at a greater risk of stroke than those with influenza, as Parikh and his co-authors discuss in their paper. They note, for example, that acute viral infections, including the flu, are known to trigger an inflammatory response in the body that can lead to blockages in blood vessels. It could be that COVID-19 initiates a particularly vigorous inflammatory response, leading to even more dangerous results.

COVID-19 also tends to be, on average, a more severe respiratory illness than influenza, with complications that put more demands on the cardiovascular system  and that, as a result, make stroke more likely.

FMI: You’ll find an abstract of the study on JAMA Neurology’s website, but the full study is behind a paywall.