The word "quarantine" would seem to have a straightforward definition: It's when a sick person is shut in for a period of time—perhaps with yellow tape or a sticker on the door—until he or she is cured or can no longer spread the disease.
But with the Ebola epidemic, the meaning of quarantine is not nearly so clear.
That's partly because Ebola patients aren't contagious until they've started exhibiting symptoms such as fever, vomiting, and diarrhea. Someone may be incubating the disease for a week or more without knowing it, potentially putting others at risk. And yet locking up everyone returning to the U.S. from the three Ebola-stricken countries in West Africa seems pointless if they can't pass on the disease anyway.
On the other hand, Ebola is contagious enough that it's infected six Americans working in West Africa and two Dallas nurses who treated a Liberian who came to the United States with the disease, Thomas Eric Duncan.
In recent days, public health officials and the public have struggled with the complexity of how to isolate those who may have been exposed to Ebola and who could be at risk for spreading it while preserving individual rights and tamping down irrational fears.
Many have criticized American doctor Craig Spencer for taking the New York subway and visiting a bowling alley the day before he was diagnosed with Ebola—and before he had symptoms.
At the same time, public health officials said it was absurd to lock up nurse Kaci Hickox in a hospital tent after she returned from treating Ebola patients in West Africa.
In an editorial published Tuesday, the prestigious New England Journal of Medicine said such quarantines are "not scientifically based" and are "unfair and unwise."
Hickox had no symptoms, though an early check at the airport recorded a moderate fever. She has since been released to her home state of Maine, where health officials say they presume she'll agree to a voluntary quarantine.
Along with Spencer's and others, her case and is raising questions about what quarantine really means and about what isolation requires to be effective.
U.S. Centers for Disease Control and Prevention director Thomas Frieden announced new federal criteria on Monday for monitoring people who are returning from West Africa or who have been exposed to Ebola in the U.S.
Frieden broke these people into four groups, depending on their risk, and said their standard for isolation should vary by their experiences.
Those at the highest risk, including people who have been stuck with patient needles or who cared for an Ebola victim without protection in West Africa, should voluntarily isolate themselves, Frieden said.
That means avoiding large gatherings and mass transportation. Solitary jogs and car rides, like the one NBC News chief medical correspondent Nancy Snyderman took to a nearby restaurant during her own self-quarantine, would be okay as long as the person doesn't have Ebola symptoms, such as fever.
The next category includes people who share a household with an Ebola patient but didn't provide direct care, like those living with Duncan—none of whom caught the disease—as well as aid workers in West Africa, such as Spencer.
Frieden said about 46 such health care workers have returned to the U.S. from West Africa since October 11, out of about 800 travelers from the affected countries. In the West African countries Liberia, Sierra Leone, and Guinea, Ebola has infected more than 10,000 people, killing 5,000.
Frieden said that health care workers returning from the Ebola zone will be monitored daily for 21 days, the Ebola virus's longest potential incubation period, and will check in with a health care worker who will either take their temperature or watch while they do it and will ask about symptoms like fatigue.
Their activities will be reviewed and permission given, depending on "what makes sense for that individual at that time," Frieden said. Someone who feels fine during their third week at home, after the highest risk period has passed, might be given more flexibility than someone feeling fatigued and who has been back only a week.
People in the low-risk category, such as health care workers who treated Ebola patients here in the United States with full protective gear, will be asked to monitor their temperatures twice a day looking for any spikes that might indicate the onset of Ebola's contagious phase.
Those at no clear risk because they had not been in close contact with someone sick with Ebola or their body fluids, such as the taxi driver who drove Spencer home from the bowling alley, do not need any restrictions at all, according to the new CDC standards.
Heroes, Not Pariahs
In making the announcement Monday, Frieden spoke about balancing the need to protect the public without feeding public panic.
"We believe these [guidelines] are based on science," he said, adding that he wanted to avoid treating health care workers returning from West Africa's Ebola zone as "pariahs, instead of recognizing the heroic work they're doing."
If quarantine requirements are too stringent, he said, people will lie to cover up their exposure, raising the risk of transmission. And he warned that health care workers might be unwilling to help out in West Africa, making it more likely the disease will keep landing on American shores.
Frieden said he expects that people will voluntarily comply with the new guidelines, though states have legal authority to make them comply if needed.
Health authorities have long favored voluntary isolation, mostly for practical reasons. "If you make people feel as if they will be stigmatized and outcast and scapegoated, they're not going to come forward the next time someone gets sick, and that would be a disaster," said Wendy E. Parmet, director of the health policy and law program at Northeastern University in Boston.
The new federal guidelines seem designed to take the pressure off governors, who have been struggling to find the right balance between voluntary and enforced isolation. After strongly supporting mandatory quarantines along with New Jersey Governor Chris Christie, New York Governor Andrew Cuomo tried to strike a moderate tone on Sunday.
Christie also softened a bit Monday, allowing nurse Kaci Hickox to leave a New Jersey hospital and return to Maine, though he defended his mandatory quarantine policy on Tuesday. Cuomo said that the government will pay workers for time missed while under quarantine.
In Georgia on Monday, the governor announced a more stringent plan, calling for mandatory quarantine of people who have had direct contact with Ebola patients from the three affected West African countries, though health care workers are exempt.
Others, including the governor of Virginia, appeared to be considering different standards.
Most public health experts appear to side with George Risi, an infectious disease doctor in Montana who slept in the spare room and didn't hug his wife and son for a week after treating Ebola patients in Sierra Leone.
He also skipped seeing patients, though he did go into his office. Risi was mindful of staying at least 3 feet from his coworkers, particularly for the first week, when he was most likely to come down with the disease if he'd caught it in West Africa.
Doing more than that is giving into public fear, Risi said, without providing any benefit to the public and likely harming West Africa.
"No one's going to want to go over there," he said, "if they have to spend 21 days in some remote hotel in New Jersey just because they've been helping."