Four military bases in Texas, California and Colorado were preparing to house American citizens for up to two weeks as part of a highly unusual federal effort aimed at slowing the spread of the deadly coronavirus. As of late Monday, though, expectations that a large number of Americans who had traveled to parts of China might quickly be held under quarantine had not come to pass.
No new travelers from China had been brought to the military bases, federal officials said. The only people under federal quarantine were fewer than 200 people who had been in Wuhan, China, the epicenter of the coronavirus outbreak, and were flown to a base in Riverside, Calif., last week.
About 250 other Americans who had recently spent time in China and showed signs of symptoms were considered “patients under investigation” by the Centers for Disease Control and Prevention and have been monitored, the federal authorities said.
“This is an unprecedented situation, and we’ve taken aggressive measures,” said Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, part of the C.D.C.
The Trump administration ordered that as of Sunday afternoon, any American citizen who in the last two weeks had visited the Hubei province, whose capital city is Wuhan, was subject to a quarantine of up to 14 days after arriving in the United States.
It remained uncertain how extensive the quarantine would ultimately become, and how many Americans would be affected. Major domestic airlines have already canceled flights to and from China as information has emerged about the outbreak that has killed hundreds and sickened thousands. The United States had 11 confirmed cases of the coronavirus on Monday evening.
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The State Department will be transporting more people back to the United States from Wuhan, Dr. Messonnier said, and the C.D.C. has sent four teams to Defense Department locations where their flights will land. She said she did not know yet how many passengers would be returning.
A federal quarantine has not been instituted in more than half a century, and brings considerable logistical challenges, legal implications and strains to local authorities.
Dr. Messonnier said the C.D.C. had been working with state and local health departments to find places to keep people under quarantine. Possibilities, she said, could include other military bases and hotels, and could vary from state to state.
Passengers from parts of China other than Hubei province who have symptoms like a cough or fever will be given medical exams, and what happens next will depend on the results of those exams. United States citizens who have visited mainland China will undergo a health screening and can be ordered to quarantine in their homes for up to 14 days, according to the Homeland Security Department. If the passengers display symptoms of the virus, they will be moved to a nearby hospital, where they will be isolated from other patients. It was not clear exactly what home quarantines would entail, or how they would be enforced.
The federal government has the power to declare a quarantine under the 1944 Public Health Service Act, an authority that derives from the commerce clause of the Constitution. According to the law, the secretary of health and human services is authorized to act to prevent the transmission and spread of communicable diseases into the United States and between states.
But the federal government’s quarantine authority is effectively limited to people coming into the country at the border, and it has rarely been exercised. More commonly, the C.D.C. has given responsibility to states, which have broad powers to quarantine people under the 10th Amendment and are better equipped to handle public health emergencies, said Lawrence Gostin, a law professor at Georgetown University and an expert on public health.
During an Ebola outbreak in 2014, a nurse who was held in quarantine in New Jersey for three days after returning from working with patients in West Africa filed a lawsuit against New Jersey. She ended her state lawsuit in 2017 with a settlement that suggested legal rights for people in quarantine.
Howard Markel, a medical historian at the University of Michigan and the author of “Quarantine!,” a history of typhus and cholera epidemics in New York City in 1892, said he believed that the current quarantine was a prudent decision, given the spread of the virus. But the process, he said, can have lasting effects.
“You can never ameliorate the experience of a quarantine,” Dr. Markel said. “Nobody who comes out of a quarantine says, ‘That was fun.’ It’s psychologically damaging.”
The current quarantine order has required a complex, multiagency effort that officials were scrambling over the weekend to put into place.
The Transportation Security Administration has directed airline carriers to determine if passengers had traveled to China before allowing them to board flights, a Homeland Security official said. Customs and Border Protection officers have also been told to question travelers upon their arrival at some airports and comb through a travel history database to determine if they were in China, the official said.
Tony Reardon, the president of the National Treasury Employees Union, which represents Customs and Border Protection officers at airports, said the Homeland Security agency was allowing officers to wear protective equipment, such as gloves and respiratory masks, while they process travelers coming from China.
Efforts to slow the virus’s spread in the United States have already proven costly. The Department of Health and Human Services informed Congress on Sunday that it may transfer up to $136 million to help combat the spread of coronavirus, according to a person familiar with the notification.
Around the country, as the four military bases were readied to receive quarantined travelers, officials sought to reassure residents living nearby. At Joint Base San Antonio in Texas, guests at two inns on the base were being relocated to make room for people who could be brought in for quarantine. At Travis Air Force Base in California, officials said a “safety cordon” would be put in place to separate evacuees from people on the base.
“This doesn’t seem like a smart plan,” one person posted on the San Antonio base’s Facebook page. “There was not a better alternative than exposing our military and their families?!”
Officials at Joint Base San Antonio, who did not immediately respond to an interview request, promised to hold town hall meetings to address residents’ fears about the quarantine.
“We hear and understand the concerns of our community and family members,” the base’s Facebook feed said in reply to commenters who questioned the decision.
In the hours and days before formal quarantine rules went into effect on Sunday afternoon, many families who had been traveling in China raced to get back to the United States. That left individual passengers to decide how much risk they personally posed to the public. Some families who had returned from China in recent days placed themselves in an informal, self-imposed quarantine, staying away from friends, co-workers and other family members out of caution.
Victoria Griffin, a teacher at a school in China, flew from Beijing to Chicago with her 19-month-old son, Teddy, on Sunday, planning to stay with her parents to avoid coronavirus back in China.
She and Teddy have had her childhood home to themselves. Her parents decided to temporarily stay elsewhere.
“Of course I would love to be with them,” Ms. Griffin said, adding that she and Teddy have been doing little but sleeping, eating and playing with toys stocked at the house. “But I do think it’s for the best.”
In Massachusetts, a toddler and his father, who may have shared a plane flight with a man who has been confirmed to have coronavirus, have isolated themselves in the basement of their Winchester home since returning from China on January 28.
The man’s wife, who asked not to be identified by name, said that the family had already been planning to isolate themselves for a period of time because of the outbreak. When they realized that her husband and their toddler may have been on the same plane as the student who was confirmed sick, their concerns grew.
Each day, the woman said, she dons a mask and gloves, and descends the stairs to bring her husband and son food.
“It’s hard, but we are trying to avoid any direct contact,” she said.