Travel restrictions from China haven’t been ruled out as the United States monitors the spreading outbreak of coronavirus that infected thousands there, Health and Human Services Secretary Alex Azar said Tuesday.

For now, the U.S. government is expanding screenings of travelers from China in order to quickly quarantine anyone who arrives while ill. There will now be screenings at 20 airports with quarantine facilities, up from five airports where screenings had been occurring for the past 10 days. While previously only passengers arriving from the city of Wuhan, the epicenter of the outbreak, were screened, now nearly all passengers arriving from anywhere in China will be.

The five confirmed infected people in the U.S. so far arrived in the country before they developed symptoms, so federal health officials also emphasized that the screenings would be a way to inform travelers to be on the lookout for symptoms.

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The State Department and the Centers for Disease Control and Prevention are also recommending against any non-essential travel to China and warning explicitly against travel to the city of Wuhan and the surrounding Hubei province.

While the number of cases in China has rapidly increased in recent days — with 1,700 new cases reported overnight, bringing the total to around 4,500 — Azar and other officials said that the risk to the general U.S. population remained low. They noted that relatively few Americans would likely be exposed to someone who had recently traveled in China, but warned health care providers in particular to be diligent about monitoring their contacts.

“Americans should know that this is a potentially very serious public health threat, but, at this point, Americans should not worry for their own safety,” Azar said.