The US Centers for Disease Control and Prevention has issued the first federal quarantine order in more than 50 years for 195 Americans who were evacuated out of Wuhan, China, the epicenter of the 2019 novel coronavirus outbreak (2019-nCoV)

The US citizens will be held under quarantine at the March Air Reserve Base in California, where they arrived from Wuhan on Wednesday, January 29 on an aircraft chartered by the US State Department. They have remained at the base since then. The quarantine will last 14 days from the time that their flight left Wuhan. Fourteen days is considered the likely maximum time of a 2019-nCoV infection incubation period—that is the time between an exposure and onset of symptoms.

The decision to issue a quarantine comes amid the continued spread of 2019-nCoV—both within and beyond China. It also comes on the heels of a report that an asymptomatic infected person from China spread the viral illness to a 33-year-old healthy business associate in Germany. Further testing found that three other associates at the same company in Germany had also contracted the infection. All four cases were mild, and the first infected associate, who noticed symptoms on January 24, started feeling better and returned to work on the 27. The report was published yesterday, January 30, in the New England Journal of Medicine.

While it’s unclear how often asymptomatic transmission is occurring during this outbreak, the documented case raises concern that such quiet spread may thwart international outbreak control measures.

According to the latest figures, the 2019-nCoV outbreak has reached nearly 10,000 cases and 222 deaths. While nearly all of the cases are in China, the disease has spread to nearly a dozen other countries, including the US. Yesterday, the World Health Organization declared the outbreak a Public Health Emergency of International Concern (PHEIC).

Don’t be a jerk

The CDC would rather be remembered for overreacting rather than under-reacting, Dr. Nancy Messonnier told reporters in a press conference today. Dr. Messonnier is the director of the CDC’s National Center for Immunization and Respiratory Diseases.

As such, the agency decided to issue the federal quarantine. It is the first time a federal agency has issued such a quarantine since the 1960s, when one was issued over a smallpox evaluation, the CDC said. The CDC also clarified that a quarantine—cordoning of people who are not yet sick but could potentially become sick—is different from isolation orders for patients who have already been identified as being sick with a concerning infectious disease, which is more common.

So far, none of the 195 evacuated citizens have been found to be infected with 2019-nCoV. And for now, the immediate risk to the American public in general remains low, Dr. Messonnier said in the press conference today.

As the outbreak stretches on, she cautioned Americans from unnecessarily panicking over the outbreak—such as buying up surgical face masks, which are not completely effective at preventing viral respiratory infections, to protect against a virus that is not currently circulating in the US. Face masks are not recommended during normal cold and flu season, and they’re certainly not recommended now, Dr. Messonnier said.

She also warned citizens not to discriminate against any of their fellow Americans of Asian descent.

Last, Dr. Messonnier reiterated that the best way for Americans to protect their health and the health of their communities is to continue practicing good hygiene practices during this cold and flu season. That is, get a flu shot, wash your hands with soap and water frequently, don’t touch your face with unwashed hands, cough and sneeze into your elbow, and stay home if you feel ill.

Update (1/31/2020, 5:00pm ET): The Trump Administration this afternoon declared the 2019-nCoV outbreak a public health emergency in the US. The Administration announced that beginning February 2, it will enforce mandatory quarantines of up to 14 days for US citizens who recently traveled to the Hubei province, where Wuhan is located. Additionally, the administration will bar entry of non-resident foreign nationals who have traveled to China in the last two weeks and who do not have immediate family in the US. The decision conflicts with the World Health Organization, which does not recommend that countries issue any travel or trade restrictions.