The evacuees were flown on a charter flight earlier this week from Wuhan, the Chinese city at the center of the new virus outbreak. They will spend two weeks at a military base in Southern California, the Centers for Disease Control and Prevention announced.
The CDC said it's the first federal quarantine since the 1960s, when one was issued over concern about potential spread of smallpox.
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"We understand this action may seem drastic. We would rather be remembered for overreacting than underreacting," said the CDC's Dr. Nancy Messonnier.
On the flight were U.S. government employees, their families and other Americans who were living in Wuhan. Initially, health officials said the evacuees were asked to stay at March Air Reserve Base in Riverside, California, to undergo three days of monitoring and testing. Officials believe it can take up to 14 days for someone who is infected to develop symptoms.
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As of early Friday, none of the Americans housed at the base had shown signs of illness, according to Jose Arballo Jr., a spokesman for the Riverside County's public health agency. Messonnier said test results from the passengers are still coming in. All have been negative so far.
Messonnier said it's still not clear how dangerous the virus is. She said government officials were motivated to issue the quarantine order after watching dramatic increases this week in the number of illnesses and deaths reported in China.
The new virus is a cousin to the SARS and MERS viruses that have caused outbreaks in the past. Since December, it's sickened thousands, mostly in China, and killed more than 200.
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In the meantime, the State Department is preparing additional flights for Americans in Wuhan. All passengers will be screened before departing, an agency official said. The CDC is working to determine how these travelers will be processed, Messonnier said.
The U.S. has advised against all travel to China and on Thursday confirmed the country's first case of person-to-person spread of the virus, the husband of a Chicago woman who got sick after she returned from a trip to Wuhan. He is the sixth patient in the U.S., and the only one who didn't travel to China.
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At the military base about 60 miles east of Los Angeles, the evacuees are staying in hotel-style housing on the base and have spent time walking and exercising in a grassy area, some wearing masks, Arballo said. Since arriving at the base, they have been given blood tests and nose, throat and mouth swabs.
One person tried to leave the base Wednesday night and was quarantined by the county.
"This action was taken as a result of the unknown risk to the public should someone leave MARB early without undergoing a full health evaluation,'' officials said in a written statement.
The incident came as the World Health Organization declared the outbreak a global emergency after the number of cases spiked tenfold in a week.
The CDC's Dr. Martin Cetron on Friday said that incident did not drive the decision for the federal quarantine.
There are potential downsides to issuing such an order, Cetron acknowledged.
"Clearly there are consequences if it is not done properly, if it induces fear and stigma," he said.
One of the evacuees is Jarred Evans, who had moved to Wuhan several years ago to play in a Chinese football league. The New York City native played at the University of Cincinnati in 2014-15.
"I'm still wearing my mask and I'm still wearing my gloves," Evans said in an telephone interview Thursday night.
Before the outbreak took hold, Evans said people in the city of 11 million people were happy as they prepared for the Lunar New Year holiday season.
Then Chinese government shut down the city, banning buses, trains, taxis, and personal cars and the military patrolled some streets. He compared its deserted atmosphere to an Old West ghost town.
"Imagine New York City being shut down," he said. "I was completely scared at first, because I didn't know exactly what was going to happen."
He said the passengers on the charter flight cheered and applauded when the jet landed at the California base after a refueling stop in Anchorage, Alaska.
Evans said he's not used to being confined.
"'But to protect myself, I have to do it," he said.
The Associated Press contributed to this report.