Editor’s note: This story, originally published on the afternoon of Jan. 22, was updated the afternoon of Jan. 24 to reflect the most recent numbers, a second U.S. patient, the current extent of travel restrictions in and around Wuhan, and the World Health Organization’s decision to not yet declare the new coronavirus a global health emergency.

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A Snohomish County man who was diagnosed Monday with the newly discovered coronavirus after a trip to China had close contact with at least 50 people after arriving at Seattle-Tacoma International Airport on Jan. 15. Health officials announced Wednesday afternoon that they were monitoring 16 people, then updated that number later in the week.

The man has the United States’ first confirmed case of the mysterious respiratory infection, which has killed at least 41 people and infected at least 1,000 since December. A second U.S. case was discovered Friday in Chicago. While most cases have been in China — the majority in Wuhan — patients have been diagnosed in a handful of other Asian countries as well.

The patient, a man in his 30s who lives alone, had been traveling solo in Wuhan since November. He started feeling unwell, with pneumonia symptoms, several days after returning to Washington state. He has been hospitalized at Providence Regional Medical Center in Everett since Sunday, and is being monitored in a special isolation unit. He is in satisfactory condition, according to Dr. Chris Spitters, interim health officer for the Snohomish Health District.

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Public health officials aren’t disclosing where the man went after returning to Washington; instead, they are opting to contact people believed to have been near the man during that time. “If there is a location where we are concerned about potential transmission but Public Health cannot contact the individuals individually,” the agency will announce that location, Spitters said.

The 50 people are being actively monitored. “Active monitoring” means public health workers are contacting them daily to find out if they are experiencing any symptoms such as a fever or respiratory issues, said Dr. John Wiesman, the state’s health officer, at a news conference Wednesday.

Health officials from the state and the federal Centers for Disease Control and Prevention (CDC) at the news conference wouldn’t say where the Snohomish County patient flew through to get from Wuhan to Seattle but that the CDC, the airlines and state health departments are working to contact those who came into close contact with the man on his flights.

Because this virus is a coronavirus, health officials have an idea of how it will behave. Coronaviruses usually aren’t contagious until someone begins showing symptoms, said Dr. Satish Pillai, a medical officer with the CDC who is in Washington to help with the response.

How a coronavirus is transmitted is different in comparison to something like measles, which is highly contagious, Wiesman said.

“You essentially have to be in contact with somebody, within 6 feet, and they have to have enough contact with you so that [saliva] droplets are essentially coming on to you,” he said.

The CDC has updated its travel health notice from a 1 to a 2, which urges travelers to practice enhanced precautions when traveling in Wuhan, Pillai said.

Coronaviruses can be spread from animals to humans, and it is believed the virus made the jump at an animal market in Wuhan. The Snohomish County man told health officials that he didn’t visit an animal market while in Wuhan and wasn’t in contact with anyone he knew to be ill.

Wiesman urges anyone who traveled to Wuhan the past couple of months to contact a doctor or local public health department.

Chinese authorities have implemented travel restrictions in Hubei province, where an estimated 30 million people live, and all public transport in and out of Wuhan — a city of 11 million people — has been halted.

Any air travel from Wuhan is being funneled through Chicago, Atlanta, Los Angeles, San Francisco and New York. Passengers on those flights will be screened before boarding connecting flights or leaving the airports.

No other cases have been reported in Washington and nobody else in the state has been tested for the virus, Wiesman said.

Despite no other cases being confirmed so far, Wiesman said he wouldn’t be surprised if more people are sickened. “I would expect at some point we are going to have more cases in the U.S.,” Wiesman said.

To protect against the virus, officials advise treating it like a flu outbreak: Wash your hands, cover your mouth when you cough, and stay home from work or school if symptoms are showing, Wiesman said.

The county health district has set up a call center to answer questions about the coronavirus. The number is 425-388-5088. The call center will be staffed 9 a.m. to 6 p.m. daily.

The World Health Organization on Thursday opted not to declare the outbreak a global health emergency yet, with a divided committee ultimately declaring it was “too early” to make such a declaration.