Coronavirus can be spread through people who aren’t exhibiting symptoms of the illness, the director of the Centers for Disease and Control and Prevention said Thursday.

Dr. Robert Redfield confirmed reports out of China that the virus can spread when the person is still asymptomatic, according to CNN.

“There’s been good communication with our colleagues to confirm asymptomatic infection, to confirm asymptomatic transmission, to be able to get a better handle on the clinical spectrum of illness in China,” Redfield told the outlet.

Redfield said it’s not known how much the asymptomatic cases are contributing to the spread of the virus — which has sickened more than 60,000 people worldwide — but the discovery is concerning.

“What I’ve learned in the last two weeks is that the spectrum of this illness is much broader than was originally presented. There’s much more asymptomatic illness,” he said.

He added that a number of confirmed cases presented with just a “little sore throat.”

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His comments come as the agency confirmed the 15th case of the coronavirus in the US.