The US Centres for Disease Control and Prevention have announced America's first reported case of the Wuhan coronavirus, which has infected more than 300 people and killed at least six in China.
The infected man was admitted to hospital on Sunday, after arriving from Seattle from Wuhan, China, on January 15, officials from the health authority said on Monday.
The man, who is in his 30s, is a resident of Snohomish County, Washington state.
The Chinese city was where the virus was first reported last month, and the outbreak was traced to a seafood and poultry market there.
The man was not identified further by local officials and is said to be responding well to treatment.
He was taken to hospital with pneumonia last week and the coronavirus infection was confirmed on Monday.
"He reported that he did not visit any of those implicated markets and did not know anyone that was ill," local health officer Chris Bitters said. "He was just travelling from that area."
The agency said it was preparing for more cases of the outbreak and raised its alert for Wuhan to level two, meaning travellers should avoid contact with sick people, animals or animal markets.
Dr Nancy Messon, a respiratory diseases expert with the centres, said she expected more cases of the virus to be identified in America and globally.
The virus has spread from Wutan to Beijing, Shanghai and Shenzhen. It has also travelled to Taiwan, Japan, Thailand and South Korea.
It has caused alarm because of its connection to severe acute respiratory syndrome, or Sars, and experts believe it may be more prevalent than realised.
Last week, the health authority began screening travellers from China at airports in Los Angeles, New York and San Francisco.
On Tuesday, the agency said it would also include these checks at Hartsfield-Jackson International Airport in Atlanta and O'Hare International Airport in Chicago.
Although US health officials said they were taking action to protect the public, they considered the risk of the virus to be low.
They said they were taking extra steps to prevent the disease from spreading to hospital staff.
Wuhan has a population of more than 11 million and Chinese officials confirmed on Monday that the virus was contagious between humans.
The World Health Organisation will hold an emergency committee on Wednesday to discuss the outbreak.