Sens. Amy Klobuchar (D-Minn.) and Marco Rubio (R-Fla.) are asking the Centers for Disease Control and Prevention (CDC) to assess the risk of strokes in younger and middle-aged coronavirus patients.

“We believe it is critical that the CDC evaluate the prevalence of stroke in COVID-19 patients, including the potential link to stroke from the development of blood clots caused by the virus,” the two wrote in a letter to CDC Director Robert Redfield.

“With over one million confirmed COVID-19 cases in the United States as of May 13, even a relatively low prevalence of stroke in this particular patient population could lead to a significant increase in the number of stroke patients in our country,” they added.

The two ask whether the CDC currently has any preliminary data on a potential coronavirus-stroke correlation, and whether it is working to obtain further data.

They further ask whether the CDC plans to update educational materials on strokes for health professionals and patients to include coronavirus-related information, even for patients who do not present typical risk factors for strokes, and what steps the agency can take to educate Americans about the potential risks.

In April, Thomas Oxley, a neurosurgeon at New York’s Mount Sinai Health System, told CNN he and colleagues have treated abut five partially or entirely asymptomatic coronavirus patients under 50 who suffered increased clotting in large arteries, which caused severe strokes.

“Our report shows a seven-fold increase in incidence of sudden stroke in young patients during the past two weeks. Most of these patients have no past medical history and were at home with either mild symptoms (or in two cases, no symptoms) of COVID,” Oxley told CNN.

Both strokes in general and large-vessel strokes in particular are typically extremely rare in patients between 30 and 40, according to Oxley, who said that over the previous 12 months he and his team treated an average of 0.73 patients under 50 per two weeks for large-vessel strokes.