US health officials have confirmed the first instance of person-to-person transmission of coronavirus in the country on the heels of a World Health Organization declaration that names the 2019 Novel Coronavirus (2019-nCoV) a public health emergency.

All previous US cases had been associated with travel to Wuhan, China, where an outbreak of respiratory illnesses associated with the virus has been ongoing since December 2019. The newly identified Illinois patient had no history of traveling to Wuhan but shared a household with a person diagnosed with the infection on January 21. Both patients are in stable condition, but the Centers for Disease Control and Prevention (CDC) says that it is closely working with state and local partners to monitor the contacts of patients diagnosed with the virus.

“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,” said CDC Director Robert R. Redfield, MD, in a statement. “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.”

The news comes as the US State Department authorized diplomatic staff and their families to evacuate China due to the virus, Axios first broke. The first case of coronavirus in the US was reported in Washington state on January 21 after the unnamed man had returned from China earlier this month.

Chinese health officials reported thousands of infections in at least 29 provinces of China, as well as Hong Kong and Macao, as the virus has been spreading from person-to-person in-country, the CDC reports. Major cities across the nation have been quarantined, and Russia announced today that it was closing its borders to China, reported Russian news agency TASS. A growing number of cases have been reported in a number of locations around the world, including much of Asia, the US, Europe, Australia, and the Middle East. (You can take a look at this live map to track the latest updates from the outbreak.)

The first reported cases of the virus were linked to workers at a market selling wild animals for food, including snakes. Researchers believe that snakes may have acted as a reservoir for the virus before jumping to humans. Coronaviruses are a large family of viruses that begin in animals and are rarely transmittable to people – even rarer are cases where the virus can evolve from person-to-person. Such was the case during the Middle East respiratory syndrome (MERS) outbreak in 2012 and the 2003 outbreak of severe acute respiratory syndrome (SARS), according to the CDC.

2019-nCoV is resulting in quarantines around the world. Just today, an estimated 6,000 passengers and crews aboard a cruise ship in Italy are being quarantined and held on the ship while medical teams run diagnostic tests on a 54-year-old person of Chinese nationality and their companion, USA Today confirmed with the cruise line.

In an attempt to combat the deadly virus, an Australian lab has grown the first coronavirus and shared cultures worldwide in an attempt to develop a vaccine. Experts say the best way to prevent infection is to avoid being exposed and to practice preventative actions like washing hands regularly, avoid touching the eyes, nose, and mouth, and avoid coming into contact with people who are sick. If a person is sick, they are advised to stay home.