“We’re very comfortable the patient is isolated and poses little risk to the staff or general public,” said Dr. Chris Spitters, health officer at the Snohomish Health District, adding that the strict isolation practices were implemented in “an abundance of caution.”

News of the first case of the virus in the United States surfaced as officials studied growing evidence that the disease can be transmitted from person to person, although it is not clear how easily.

“There is new information hour by hour, day by day, that we are tracking and following closely,” said Dr. Nancy Messonnier, director of the C.D.C.’s National Center for Immunization and Respiratory Diseases.

The C.D.C. has deployed staff overseas who are working closely with the ministries of health in China and Thailand. “The key issue we all need to understand is how easily and sustainably the virus is spread from human to human,” Dr. Messonnier said.

Federal health officials plan to expand the screening of passengers arriving in the United States from Wuhan to five airports that are major international hubs. All travelers from the city will be funneled through those airports.

Screenings started on Friday and Saturday at New York’s Kennedy International Airport, San Francisco International and Los Angeles International. Now they will be expanded to Hartsfield-Jackson Atlanta International and Chicago O’Hare International over the next few days.

Passengers from Wuhan planning to arrive in other cities will be issued new tickets taking them to one of the five screening airports, officials said.