When COVID-19 patients began flooding emergency departments at New York hospitals in March, doctors saw some unusual cases of stroke.

“We had a young woman in her early 30s who came in with a profound stroke, the kind of stroke that leaves someone permanently paralyzed and possibly unable to survive,” says Dr. J. Mocco, a professor of neurosurgery and director of the cerebrovascular center at Mount Sinai Health System in New York.

Her stroke was caused by a blood clot that was restricting blood flow to the right side of her brain. The young woman had none of the usual risk factors for stroke. But she tested positive for SARS-CoV-2, the coronavirus that causes COVID -19.

And so did several other young, otherwise healthy people who had been admitted for major strokes. So Mocco and other doctors in the hospital system began to compare notes.

“Speaking with the ICU doctors and the pulmonary doctors, they were seeing clots in the lungs,” he says. “Speaking with the renal doctors and the dialysis doctors, they were seeing clots in the renal arteries causing kidney injury.”

Mocco and his colleagues thought it was time to sound the alarm. So they published a letter Tuesday in The New England Journal of Medicine describing five patients in their 30s and 40s who did not have the typical risk factors, but did have the SARS-CoV-2 virus.

The letter was the latest evidence of a phenomenon doctors have been reporting since the early days of the pandemic in China. COVID-19 seems to produce blood clots — a lot of them. And this has been especially well documented in intensive care units. . .

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