"This is a rapidly changing situation, both overseas and domestically", said Messonnier. People that the women had close contact with are being monitored. At least 60 people are "under observation" in 22 US states. To date 11 of them have been ruled out, having tested positive for other respiratory illnesses.
"We are working to continue respirator production during the Chinese New Year holiday", she said.
The woman is hospitalized in isolation.
Tests on 14 people in the United Kingdom returning from the area have so far come back negative, but Professor Paul Cosford, medical director at Public Health England, told BBC News that it's "highly likely that we will have cases in the United Kingdom".
"There are still many missing pieces in the jigsaw puzzle to fully understanding this new virus which is spreading rapidly across China, and most probably around the world", Peter Piot, Professor of Global Health and Director at London School of Hygiene & Tropical Medicine, commented on Friday. It infected more than 8,000 people and killed 774 - and then it disappeared, thanks to public health measures.
The People's Daily reported that China's southern Guangdong Province had 53 confirmed cases across 11 cities by January 23. WHO Director-General Tedros Adhanom Ghebreyesus was keen to stress that the decision was not final, while urging countries to take steps to limit the virus' spread. It's still hanging around, causing small numbers of infections each year: The World Health Organization has counted almost 2,500 cases of MERS in the Middle East and beyond, and more than 850 deaths. At least 26 people have died. It has now spread to neighboring countries across Asia and into the US.
The new virus comes from a large family of coronaviruses, some causing nothing worse than a cold. There are two ways this outbreak could pan out.
The World Health Organisation surprised many on Thursday by announcing they are not now classing the virus as an "international emergency".
Tedros Adhanom Ghebreyesus, the World Health Organization director-general, said the outbreak is an emergency in China, but doesn't yet constitute a global crisis.
"It may yet become one", said the WHO's boss. A number of major airports have started screening passengers inbound from Wuhan. Those airports were San Francisco, Los Angeles, John F. Kennedy in New York, Atlanta, and Chicago O'Hare. Like the U.S., Taiwan has reported one case.
Coronavirus is a respiratory illness common in animals and humans, but the new strand, called novel coronavirus 2019, has not been previously detected, according to the CDC.