(CNN) The new coronavirus appears to be causing sudden strokes in adults in their 30s and 40s who are not otherwise terribly ill, doctors reported Wednesday.

They said patients may be unwilling to call 911 because they have heard hospitals are overwhelmed by coronavirus cases.

There's growing evidence that Covid-19 infection can cause the blood to clot in unusual ways, and stroke would be an expected consequence of that.

Dr. Thomas Oxley, a neurosurgeon at Mount Sinai Health System in New York, and colleagues gave details of five people they treated. All were under the age of 50, and all had either mild symptoms of Covid-19 infection or no symptoms at all.

"The virus seems to be causing increased clotting in the large arteries, leading to severe stroke," Oxley told CNN.

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