A newly identified coronavirus that has infected more than 300 people in China has spread to the United States, the Centers for Disease Control and Prevention (CDC) will report on Tuesday as public health officials confirmed the virus is transmitting between humans.

The virus, initially called 2019-nCoV, was identified in December in Wuhan, China. Dozens of cases have been identified in other major Chinese cities including Beijing, Shanghai and Guangzhou. Four cases have been identified outside the country, in Japan, Thailand, South Korea and Taiwan. At least six people have died.

The CDC will say Tuesday that at least one case has been identified in Washington state, according to a source familiar with the agency’s plans. CNN and The New York Times first reported the case, though details about the patient’s identity were not immediately clear.

The patient is a 30-year-old man who had recently traveled from Wuhan to the U.S., a CDC official said Tuesday.

He is in good condition and currently hospitalized "out of an abundance of caution" and short-term monitoring, the CDC said. 

The patient entered the U.S. before the airport screening was implemented last week and didn't experience any symptoms until later.

The CDC said it’s still unclear how easily the virus is spreading between people but believes the risk to the American public at large “remains low at this time.”

Investigators are looking for people who have may come into contact with the patient to determine if anyone else has become ill.

CDC workers have been deployed to support the investigation in Washington.

The CDC noted that while the illness has caused some deaths, other patients have had milder symptoms and have been discharged.

Symptoms include fever, cough and trouble breathing.

Wuhan’s Municipal Health Commission said Monday that at least 15 medical workers have tested positive for the virus, The Associated Press reported, a troubling sign that the virus is spreading between humans.

The CDC last week began screening travelers from Wuhan arriving at three U.S. airports.

In China, officials are worried that the coming Chinese New Year could offer the virus an opportunity to spread far beyond Wuhan, as people travel across the country to be with their families. Chinese President Xi Jinping called for “all-out efforts” to prevent and control the virus, the National Health Commission said in a statement Tuesday.

A top World Health Organization panel will meet Wednesday to decide whether the virus should be declared a public health emergency of international concern.

Coronaviruses are common in animals like bats, cats and camels, according to the CDC. The family of viruses also cause the common cold.

In rare occasions, coronaviruses from animals can spread to humans in what are called spillover events, when a virus jumps between species. An outbreak of severe acute respiratory syndrome (SARS) infected more than 8,000 people in 37 countries in 2002 and 2003. Middle East respiratory syndrome (MERS) spread from camels to humans, has infected about 2,000 people in the last decade, mostly in Saudi Arabia and South Korea.

The current virus appears to be less deadly than SARS or MERS, experts said, though the human-to-human transmission raises concerns that it could spread just as widely.

The current outbreak likely started in a wet market, places common in China where animals are sold in the open. Chinese officials have shuttered wet markets in Wuhan and the surrounding province.

“Live animal markets are areas where you can get the spread of new or existing viruses, or renomination of flu viruses, which is one of our real fears,” said Tom Frieden, the former CDC director who now runs Resolve to Save Lives, a global public health nonprofit.

Tarik Jasarevic, a spokesman at the WHO, said scientists are still looking for the animal source of the new virus. Chinese officials alerted the WHO about the new virus on Dec. 31. Days later, they posted the virus’s genetic code to an international health website to facilitate diagnosis and research into potential treatments.

China’s response to the virus is a marked contrast from two decades ago, when the government tried to keep the growing SARS outbreak quiet. This time, Xi and Premier Li Keqiang have ordered local governments to identify and report cases, and to work with the WHO and neighboring countries to contain the spread, the National Health Commission said. Li held a high-level meeting of government ministers to address the crisis on Monday.

“China quite quickly identified a new virus and identified it as a new coronavirus,” Jasarevic told The Hill on Sunday. “To their credit, they shared the genetic sequence.”

Frieden, the former CDC director, said the new virus and its spread beyond China’s borders should serve as a wake-up call to the global public health community. In an era of globalization and widespread travel, a virus in Wuhan can threaten other parts of the world in a matter of days or weeks.

“China has had the wherewithal to identify the cluster and this organism, but how many other things like this are spreading in Asia or Africa and not getting investigated?” Frieden said. “There's a massive amount of travel around the world. That's why it's in all of our interest that the public health equivalent of a smoke alarm or a sprinkler system is present everywhere.”

“There are always going to be new threats coming out of the microbial world, and we need to be better prepared than we are today,” he said.