The Centers for Disease Control and Prevention on Tuesday confirmed the first U.S. case of a new coronavirus that has killed six people in China.

The CDC and Washington state officials said the man, a Snohomish County resident in his 30s, was in good condition at Providence Regional Medical Center in Everett. The symptoms presented Sunday, and the diagnosis was confirmed Monday.

Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, called the news "concerning," particularly in light of reports that the virus has begun to spread from person to person.

"The confirmation of human-to-human spread in Asia certainly increases our concern," Messonnier said.

Washington Gov. Jay Inslee said Tuesday that he expected more cases in the U.S.

"Based on what we know now, risk to the general public is low," Inslee said in a statement. "We take this very seriously and, while this is the first case in the U.S., there will likely be others."

The CDC, which began enhanced health screenings last week at airports in San Francisco, New York and Los Angeles, said Atlanta and Chicago would be added to the list. All traveling from Wuhan, China – where the outbreak began – to the U.S. are rerouted to these airports.

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Hundreds of people in China have been diagnosed with the virus in the past few weeks. Most of the cases were reported in the central city of Wuhan. It spread to other areas of the country, and a handful of cases have been diagnosed in Thailand, South Korea and Japan.

The World Health Organization is gathering a panel of experts on coronavirus Wednesday in Geneva to determine whether the outbreak constitutes an international public health emergency and how it can be managed.

Many of the initial cases were linked to a seafood market in Wuhan. Chinese health officials said this week that human-to-human transmission has been confirmed.

The coronavirus may lead to a severe form of pneumonia that could be deadly, said Robert Glatter, an emergency physician at New York's Lenox Hill Hospital. People with a history of chronic lung disease may be at higher risk for "adverse outcomes," he said.

"We must be vigilant to ensure that adequate screening processes are in place at all US airports," Glatter said.

Coronaviruses are a large family of viruses that cause illness ranging from the common cold to more severe infections such as pneumonia; Middle East respiratory syndrome, known as MERS; and severe acute respiratory syndrome, or SARS. Common signs of infection include fever, cough, shortness of breath and breathing difficulties. In more severe cases, infection can cause kidney failure or death.

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The virus can spread from animals to people. It can be spread by coughing, sneezing and through close contact with an infected person or an object carrying the virus.

Coronaviruses, Ebola and SARS are zoonotic, meaning they are transmitted between animals and people. Ebola was carried by fruit bats, which spread it to other animals. SARS was transmitted from civet cats to humans and MERS from camels to humans.

There is no vaccine, although nine studies are examining coronavirus vaccine development. Although there is no specific treatment for the coronavirus, recommended measures are similar to those for a cold, such as rest and drinking a lot of fluid.