SEATTLE — Health officials scrambled on Wednesday to contact more than a dozen people who may have been exposed to the United States’ first case of the Wuhan coronavirus, even as regulators sought to assure the public there was little risk from an illness that has rapidly spread across Asia, killing at least 17 people.
The patient, a man in his 30s who fell ill after traveling to China, has cooperated in helping public health workers trace his path from the Wuhan region of China to his home in Snohomish County, Wash., north of Seattle, health officials said.
Officials said they have been working to identify people who had close contact with the patient once his symptoms began to flourish. They do not believe he was symptomatic on his travel home, but the state health department said that out of “an abundance of caution,” the Centers for Disease Control and Prevention would notify passengers on his flight.
The primary focus, however, is trying to contact other patients at the clinic the man visited on Sunday, a hospital official said. He reported then that he was sick and concerned about the prospect of a coronavirus infection.
“We’re really pleased with the progress that we’re making,” John Wiesman, the secretary of health in Washington State, said at a news conference on Wednesday.
Health workers have reached out to 16 people who may have had close contact with the patient, all of them located in either Snohomish County or in Seattle’s King County. That number may grow as the investigation continues, the officials said.
They said they planned to remain in daily contact with those people to monitor any possible symptoms but have not asked them to isolate themselves, under the assumption that this variation of coronavirus, which researchers are only beginning to understand, operates like other versions that transmit only once someone becomes symptomatic.
Officials believe that the virus is transmitted through the air by coughing and sneezing, by close personal contact such as touching an infected person, and from touching a surface with the virus on it before touching the mouth, nose or eyes.
The new virus emerged in China at the end of December and spread to other countries in Asia. The outbreak, which has sickened more than 540 people and left at least 17 dead, has triggered extensive protections around the globe, including extra screening and protocols for travelers coming from the Wuhan region in China.
In the United States, passengers from Wuhan are being funneled to airports in Los Angeles, San Francisco, Atlanta, Chicago and New York, where screening stations have been set up.
Chinese authorities escalated their own actions, announcing plans to close off the city of Wuhan by canceling planes and trains scheduled to leave the area of more than 11 million people. The World Health Organization has been considering whether to declare an international emergency.
In Washington State, officials declined to discuss additional details about the patient or the specifics of his travel, saying they would publicly disclose them only if they had trouble making contact with people who might be at risk. While public health leaders said they saw minimal risk to the public, they also said the case in Snohomish County may not end up being the only one.
“We have our first case in the U.S.,” Mr. Wiesman said. “I would expect that at some point we’re going to have more cases in the U.S.”
After the first American patient visited a clinic on Sunday, a few days after returning from China, doctors asked him to stay home and isolated as they worked with the C.D.C. to test whether he had been infected by the new coronavirus.
After confirming the illness, officials later coordinated with emergency medical technicians to bring the man to Providence Regional Medical Center in the city of Everett, where a containment unit had been built during the most recent Ebola outbreaks, said Dr. Jay Cook, the hospital’s chief medical officer. The unit has a negative airflow to filter any air coming out of the room, and an adjacent room for workers to put on protective equipment if needed.
Dr. Cook said the patient was doing well under treatment by a team of caregivers that volunteered to handle patients who have illnesses of particular concern or that may be highly contagious. He said he was hopeful the patient could be discharged in the near future.
As the coronavirus has continued to spread through Asia, and as health officials try to determine how it spreads and how to contain it, regulators in the United States have sought to assure the public that there was little risk — while acknowledging that there may be anxiety about the arrival of an illness that has drawn global attention.
“I think that’s understandable given the amount of uncertainty and the new nature of this virus,” Dr. Cook said.
Symptoms of the virus include runny nose, headache, cough and fever. Officials said that anyone who feels sick should follow the usual protocols of staying home from work, covering coughs and washing hands. They said people who were ill after traveling to the Wuhan region should contact a health care provider.