The U.S. patient is responding well to treatment and was not severely ill, CDC and Washington State health officials said.
CDC officials said the agency is preparing for more U.S. cases of the coronavirus that originated in the Chinese city of Wuhan, and raised its travel alert for Wuhan to a level 2, calling for enhanced precautions. Under that alert level, the CDC recommends travelers to Wuhan should avoid contact with sick people, animals or animal markets.
"We do expect additional cases in the United States and globally," Dr. Nancy Messonnier, a CDC respiratory diseases expert said on a conference call with reporters.
CDC officials said they have begun tracking down individuals who came in contact with the patient to check them for symptoms.
Last week, the CDC began screening travelers from China at U.S. airports in New York, Los Angeles and San Francisco. On Tuesday, the agency said it will expand screening for the virus to the Hartsfield-Jackson International Airport in Atlanta and O'Hare International Airport in Chicago.
Besides the United States, cases outside of China have been reported in South Korea, Thailand and Japan.
"I don't think looking at what we know so far that this it on the scale of SARS and MERS, the two most significant coronavirus outbreaks that we know from history," Dr. Amesh Adalja, from the Johns Hopkins University Center for Health Security, said in a phone interview.
"It is early days in this outbreak and we don't have a good handle on the severity of illness," Adalja added.
On the call, CDC officials said they have screened more than 1,200 passengers since Jan. 17. None of them have been sent on for additional testing.
The U.S. traveler from Washington state had returned on Jan. 15, arriving at Seattle-Tacoma International Airport, which is not on the U.S. list for enhanced screening.
The patient sought care at a medical facility in Everett, Washington, and was treated for the illness. Based on his travel history and symptoms, healthcare professionals suspected the new coronavirus.
Specimens were taken from the patient and sent to the CDC for testing. The agency said it has developed a new test that allowed it to identify the presence of the virus in a traveler.
Washington state health officials said they are taking steps to protect the public and continue to believe the risk is low. Healthcare personnel are taking precautions to prevent the infection from spreading to hospital staff, they added.
As is often the case, preliminary information suggests older adults with underlying health conditions may be at increased risk of severe disease, CDC's Messonnier said.
The agency is working with health officials in China and globally to better understand the virus and any potential treatments.
Messonnier confirmed that the CDC is working with the U.S. National Institutes of Health to develop diagnostics and a vaccine. U.S. officials have said it could take at least a year of testing before any vaccine could be used on the public.