A United States citizen who recently returned from a trip to central China has been diagnosed with the new virus that has sparked an outbreak and stringent monitoring around the world, a spokesman for the US Centers for Disease Control and Prevention (CDC) said on Tuesday.

The man returned to the Seattle area in the middle of last week after travelling to the Wuhan area, where the coronavirus outbreak began. The man is in his 30s and is in good condition at a hospital in Everett, outside Seattle.

The US is the fifth country to report seeing the illness, following China, Thailand, Japan and South Korea.

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Late last week, US health officials began screening passengers from central China at three US airports. Officials around the world have implemented similar airport screenings in hopes of containing the virus during the busy Lunar New Year travel season.

Last month, doctors began seeing a new type of viral pneumonia - marked by fever, coughing and difficulty breathing - in people who spent time at a food market in Wuhan. More than 275 cases of the newly identified coronavirus have been confirmed in China, most of them in Wuhan, according to the World Health Organization.

The count includes six deaths - all in China, mostly among people age 60 or older, including at least some who had a previous medical condition.

Officials have said the virus probably spread from animals to people, but this week Chinese officials said they have concluded it also can spread from person to person.

In announcing the airport screenings last week, CDC officials said the risk to the US public was low, but that it was likely the illness would appear in the US at some point.