SEATTLE (AP) — The U.S. on Tuesday reported its first case of a new and potentially deadly virus circulating in China, saying a Washington state resident who returned last week from the outbreak's epicenter was hospitalized in good condition near Seattle.

The man, identified only as a Snohomish County resident is in his 30s, was not considered a threat to medical staff or the public, health officials said.

The virus has infected about 300 people, all of whom had been in China, and killed six. The newly discovered virus can cause coughing, fever, breathing difficulty and pneumonia.

Airports in the U.S. and other countries have stepped up monitoring, checking passengers from China for signs of illness. The U.S. is the fifth country to report seeing the illness, following China, Thailand, Japan, and South Korea.

Late last week, U.S. health officials began screening passengers from Wuhan in central China, where the outbreak began, at three U.S. airports — New York City's Kennedy airport and the Los Angeles and San Francisco airports. On Tuesday, the CDC announced it will add Chicago's O'Hare airport and Atlanta's airport to the mix later this week.

What's more, officials will begin forcing all passengers that originate in Wuhan to go to one of those five airports if they wish to enter the U.S.

Officials around the world have implemented similar airport screenings in hopes of containing the virus during the busy Lunar New Year travel season.

The U.S. resident had no symptoms when he arrived at the Seattle-Tacoma airport last Wednesday, but he contacted doctors on Sunday when he started feeling ill, officials said.

Last month, doctors began seeing the new virus in people who got sick after spending 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, most of them age 60 or older, including at least some who had a previous medical condition.

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

Health authorities this month identified the germ behind the outbreak as a new type of coronavirus. Coronaviruses are a large family of viruses, some of which cause the common cold; others found in bats, camels and other animals have evolved into more severe illnesses.

SARS, or severe acute respiratory syndrome, belongs to the coronavirus family, but Chinese state media say the illness in Wuhan is different from coronaviruses that have been identified in the past. Earlier laboratory tests ruled out SARS and MERS — Middle East respiratory syndrome — as well as influenza, bird flu, adenovirus and other common lung-infecting germs.

The new virus so far does not appear to be as deadly as SARS and MERS, but viruses can sometimes mutate to become more dangerous.

University of Washington coronavirus researcher David Veesler said the public “should not be panicking right now.”

The response has been “very efficient,” Veesler said. “In a couple of weeks, China was able to identify the virus, isolate it, sequence it and share that information.”

Veesler added: “We don’t have enough data to judge how severe the disease is.”

The CDC's Dr. Nancy Messonnier said health officials expected to see more cases in the U.S. and around the world in the coming days.

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Stobbe reported from New York.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.