U.S. citizens returning from other parts of China will be given health screenings, and if they have coronavirus symptoms, they'll also be placed under quarantine, in isolation. Those who don't have any symptoms and have not been in Hubei province in the past 14 days, will be allowed to move freely, with guidance to stay home when possible and monitor themselves for illness over the next two weeks.
Also Friday, the Trump administration announced that it was temporarily suspending entry into the U.S. for any foreign nationals who may be at risk for carrying the virus. The proclamation applies to anyone other than immediate family of U.S. citizens.
Over the weekend, Chinese officials criticized the U.S. for its travel restrictions. "Many countries have offered China help and support through various ways. In contrast, the U.S. comments and actions are neither based on facts, nor helpful at this particular time," China's foreign ministry spokesperson Hua Chunying said in a statement.
"We made an aggressive decision in front of an unprecedented threat," Messonnier said. She explained the measures are not intended to catch every single case of coronavirus that comes into the country, which would be virtually impossible.
"The goal," she said, "is to slow the entry of this virus into the United States."
While Chinese health authorities have said they would permit infectious disease experts from other countries to help with the outbreak, the U.S. has not yet been invited.
Messonnier suggested the CDC's invitation to China is pending.
"We have folks ready to go to China as soon as that offer is finalized," she said. "As soon as we're allowed to go, we'll be there."
Coronavirus in the U.S.
As of Monday morning, 11 people in the U.S. had been diagnosed with the coronavirus. Nine of those patients had traveled recently to Wuhan. The other two are close contacts of the patients, representing person-to-person spread of the illness in this country.
The CDC said the illnesses in the 11 patients ranged in severity. Some illnesses were mild, while others have developed pneumonia and needed mechanical support to breathe. On Monday, it was announced the first patient to be diagnosed in the U.S. — a resident of Washington state — had been released from the hospital, though he will remain in isolation at his home.
Dozens of people who came into contact with the 11 patients have been asked to monitor themselves for fever or respiratory symptoms for 14 days.
States with confirmed cases are Arizona, California (with six cases), Illinois (two cases), Massachusetts and Washington.
So far, the CDC said it's performed 260 tests sent from 36 states. The 11 known cases tested positive; 167 were negative. The rest are pending, and infectious disease experts said additional cases are expected.
Follow NBC HEALTH on Twitter & Facebook.