A Snohomish County man, the first U.S. case of the Chinese coronavirus, remains hospitalized.

EVERETT — Health officials say 43 people now are under watch because they were in contact with a Snohomish County man who tested positive for the first U.S. case of Wuhan coronavirus.

On Friday, a second case of the coronavirus was confirmed in the U.S. of an Illinois woman in her 60s.

Snohomish Health District spokeswoman Heather Thomas said Thursday the district has been working closely with other regional, state and national public health agencies with daily symptom monitoring.

On Wednesday, investigators had identified 16 people who came in close contact with the man. The number increased 27 on Thursday morning and to 43 by late afternoon. At highest risk is anyone who gets within six feet of an infected person, and especially those who have been exposed to that person’s coughing or infected droplets.

Since late Monday, the Snohomish County man in his 30s has been in an isolated room at Providence Regional Medical Center Everett, in no apparent distress, officials said. As of Thursday afternoon, no one else in Washington had tested positive for the virus.

He was not symptomatic after returning to the U.S. Jan. 15 from a trip to visit family members in Wuhan, China, the epicenter of the mysterious virus. At least 25 people in China have died from the virus, most 60 or older with some previous medical condition, and more than 800 cases there have been confirmed.

Chinese authorities Thursday moved to lock down at least three cities with a combined population of more than 18 million in an unprecedented effort to contain the virus. Other cases have turned up in Japan, South Korea, Thailand, Singapore, Vietnam and Hong Kong.

The Snohomish County man was traveling alone but took a form of group transportation home from Sea-Tac Airport. He lives by himself.

On Wednesday, the health district set up a hotline for public questions and concerns at 425-388-5088. It will be answered from 9 a.m. to 6 p.m. indefinitely.

“This morning they were getting a call every 4 to 5 minutes,” Thomas said Thursday. “Some of it’s just rumor control. A lot of it is, ‘I’ve been at this location, so do I need to be concerned?’”

So far the district has not released public locations where the man has been, as is typically done in the case of measles, an airborne illness that can linger for hours.

“The risk to the general public remains low,” said Dr. Chris Spitters, the county’s health officer. “If there is a location where we are concerned about potential transmission, and where public health cannot contact those individuals directly, that information will be released quickly.”

The man started having respiratory symptoms on Sunday and went to a health clinic. A sample was sent for testing to the federal Centers for Disease Control and Prevention in Atlanta.

On Monday, it was confirmed he had the virus. He was admitted to the hospital around midnight.

A Providence spokesman said Thursday the patient is in satisfactory condition and being monitored. The hospital is working with the state’s Department of Health and the CDC to determine when he will be discharged.

Stephanie Wright, a Snohomish County councilwoman who is the chair of the county’s Board of Health, praised the local team of medical experts and staff who have been working “pretty much around the clock.”

“They have been thrust into a national and global spotlight,” she said, “working alongside colleagues from the state and CDC to develop processes and procedures that will guide future investigation and response efforts.”

Herald reporter Caleb Hutton and the Associated Press contributed.

Andrea Brown: abrown@heraldnet.com; 425-339-3443. Twitter @reporterbrown.