The husband of one of the patients in the U.S. with coronavirus has also been diagnosed with the illness — the first evidence that the new virus has spread person-to-person in this country, the Centers for Disease Control and Prevention reported Thursday.
"We understand that this may be concerning, but based on what we know now, our assessment remains that the immediate risk to the American public is low," Dr. Robert Redfield, director of the CDC, said during a call with reporters.
The outbreak of the new coronavirus was declared a global public health emergency on Thursday by the World Health Organization.
The couple lives in Chicago. The wife had been caring for her father in Wuhan, China, earlier this month. Wuhan continues to be the epicenter of the outbreak that's now sickened upward of 8,000 people. At least 170 people have died, all in China. The woman's husband had not traveled to China.
Six people have now been diagnosed with the new coronavirus in the U.S., two each in Illinois and California, and one each in Arizona and Washington state.
Infectious disease experts said that news of the spread in the U.S. was not unexpected.
"This is nothing to be either surprised or concerned about," said Dr. Tom Frieden, former CDC director and current president of Resolve to Save Lives, a global public health initiative. But, Frieden told NBC News, "we do need to continue to look intensively to understand both how it is spreading in China and what can be done to reduce the spread."
Both of the Chicago patients are in their 60s, and the husband has underlying medical conditions, health officials said. It's believed the husband was exposed when the wife was experiencing symptoms, which include fever and cough.
Doctors said the man had not been to any large public gatherings before becoming ill.
"We are not recommending people in the general public take precautions, such as canceling activities or avoiding going out," Dr. Ngozi Ezike, director of the Illinois Department of Public Health, said during the briefing with reporters. "Be assured that we are actively monitoring all close contacts for symptoms."
Overall, 165 samples of suspected cases have been sent to the CDC for testing. Six have been positive, and 68 have been negative for the coronavirus. Test results on the rest are pending.