The agency confirmed the second coronavirus case in Chicago on Thursday.
The Illinois Department of Public Health said the woman in her 60s, who was the first case reported in Illinois, is stable and doing well. Local health officials said the patient's husband reported his symptoms on Tuesday and was hospitalized before his test results came back positive for coronavirus.
Both patients are being monitored in isolation at the St. Alexius Medical Center in Hoffman Estates, hospital officials confirmed on Thursday.
The hospital said its following infection control precautions and protocols set up by the CDC.
Officials said testing showed the man, who's in his 60s, has coronavirus, and he is also stable. The husband lived with his wife and was exposed to her after she showed symptoms and before she was confirmed to have coronavirus, officials said.
The woman had traveled to Wuhan in late December and returned to the U.S. on Jan. 13. Her husband had not traveled to China, officials said.
Local health officials said they've been closely monitoring more than 20 people in Illinois, including health care workers at St. Alexius hospital.
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Illinois Department of Public Health Dr. Ngozi Ezike said health officials are investigating locations where the second patient visited in the last two weeks, and any close contacts who were possibly exposed.
Officials said the man didn't take the CTA or attend large gatherings, but he did travel to Cleveland more than two weeks ago.
Health officials in Ohio were unable to say how he traveled, only that he had no symptoms at the time.
Local health officials emphasized that there's no health emergency in Chicago and there's low risk of contracting the new virus in the area.
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The transmission is the sixth case of coronavirus in the U.S. There are 165 people under investigation for coronavirus and 21 in Illinois.
The World Health Organization decided Thursday to declare the new coronavirus, which has sickened thousands and sparked concern around the world, a public health emergency of international concern.
The organization deliberated for two days last week on the same issue but declined to declare a global emergency at the time. Since then, however, patients from Germany, Japan, Taiwan and Vietnam have been diagnosed with the new coronavirus without having visited China. The new coronavirus is in the same family of viruses as the common cold and SARS.
At last count, more than 7,700 people have been sickened by the novel coronavirus, and 170 people have died from the disease. More than 90% of those cases, and all of the deaths, occurred in China.
"Given what we've seen in China and other countries with the novel coronavirus, CDC experts have expected some person-to-person spread in the US," CDC Director Robert R. Redfield said. "We understand that this may be concerning, but based on what we know now, we still believe the immediate risk to the American public is low."
It is likely there will be more cases reported in the U.S. in the coming days and weeks, including more person-to-person spread, health officials said.
Despite the WHO declaring a global health emergency, doctors are still cautioning the public not to panic.
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"There's no reason to curtain your daily activity or not go to work," said Dr. Igor Koralnik, an infectious disease specialist with Northwestern Medicine.
Koralnik said practicing regular daily hygiene and regularly washing your hands is your best defense.
"If you have not been traveling to China or been in close contact with somebody who traveled back from China in the zone of high rate of infection then you are not at risk of developing the infection of the coronavirus," Koralnik said.
He said right now, there are other viruses spreading faster in the Chicago area that are equally as contagious and dangerous, such as the flu.
"You have to remember that in 2019, 55,000 hospitalizations have taken place because of the flu and there were about 2,900 fatalities caused by the flu alone despite the availability of the vaccine," Koralnik said.
He said there's no need to wear surgical masks if you're not sick, especially in the Chicago area where the risk of getting the virus is low.
Koralnik and other health experts said the mask itself could become contaminated, and it can serve as a source of infection.
In light of the travel recommendation, Northwestern University has prohibited university-sponsored undergraduate travel to China. University-sponsored spring break travel to China will be redirected, as well, but summer travel to China remains on schedule.
Chicago-based United Airlines has implemented a second phase of temporary reductions in service to China, a spokesman said.
"This reduction of service, beginning Feb. 9 and running through March 28, includes 332 additional roundtrip cancellations, reducing our 12 daily departures from the United States for mainland China/Hong Kong to four daily departures," the spokesman said.
ABC News contributed to this report