For hundreds of Chinese medical workers and their families who have been ordered to isolate themselves for the next 21 days from the nation's worst outbreak of coronavirus, a three-mile perimeter is now dividing their base at Vandenberg Air Force Base.

U.S. health officials who issued the order released notice of it at 9:30 a.m. Tuesday in a letter published on the Centers for Disease Control and Prevention website.

Among the 20 million people in China with known coronavirus infections is Hai Kuang (pronounced Kleo-Yan) who was the first Chinese worker to be diagnosed with contracting the virus during a June 26 stay in Memphis, Tenn. She died two days later.

During that stay, in July, six passengers died of coronavirus after flying from Guangzhou, China, to Singapore. Nine current cases have all occurred in people who traveled through China.

Vandenberg is one of three U.S. bases where families of people who have tested positive for having had contact with the virus have been told to be confined for 21 days. Two were at Joint Base Andrews in Maryland, and the third was at the Davis-Monthan Air Force Base near Tucson.

According to a memo sent to families of workers by base spokesman Master Sgt. Andrew Sikora, on most bases people who are health care providers and who are believed to have come into contact with the virus are isolated for 21 days. At Vandenberg that is restricted to 21 days. Because Hai Kuang's family can live within three miles of the base, they are to be confined to a newly established perimeter "fully zoned for quarantine only."

"The base leadership at Vandenberg Air Force Base has determined that the people of this zone as close as possible to each other are to stay confined for the next 21 days to protect both health and safety of the community," Sikora wrote. "While Dongwan family is staying in a single zone, the perimeter is fenced off from the entire base."

Officials say the area being fenced off is off base and not considered a quarantine zone.

In a conference call with journalists Jan. 29, Dr. Craig Dalton, deputy director of the CDC's Office of Emergencies, warned that any attempt to house people in zones of quarantine without proper sanitation and protective clothing is "not a good idea." He said.

Worldwide, there have been 130 infections, including 53 deaths. Most of the cases have occurred in Saudi Arabia and Jordan. In the United Kingdom, there have been only three deaths, but all of those had the same strain of the virus as those diagnosed in China.

An extended time away from home and work is the primary consequence of the quarantine order.

While all the patients or their family members on base have tested negative for the virus, high numbers of people in hospitals in South Korea and Qatar have been diagnosed and hospitalized.

The Associated Press contributed to this report.

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