Nurse Kaci Hickox has defied the Ebola quarantine order, leaving her house in Maine for a brief bike ride.
She returned from treating Ebola patients in Sierra Leone on October 24.
Kaci Hickox maintains isolation is unnecessary, as she has no symptoms and has tested negative for Ebola.
Maine officials have vowed to go to court to try to enforce the quarantine.
About 5,000 people have died of the disease in West Africa, but only nine patients have been treated for the virus on US soil.
More than 13,700 people have been sickened in the Ebola outbreak, the vast majority in Liberia, Sierra Leone and Guinea.
Ebola, which is only spread through close contact with the bodily fluids of a sick patient, has a 21-day incubation period.
US officials are at odds over whether American healthcare workers who return from treating Ebola patients in West Africa should be forced into quarantine until that period has expired.
New Jersey and other states had put quarantine rules into place after a New York doctor who treated Ebola patients in West Africa came down with the disease.
The US Centers for Disease Control and Prevention (CDC) merely recommends daily monitoring of returned health workers, rather than enforced isolation.
President Barack Obama has warned that overly restrictive measures imposed upon returning healthcare workers could discourage them from volunteering in Africa.
“We know that the best way to protect Americans ultimately is going to stop this outbreak at the source,” he said on October 29 .
Kaci Hickox returned to the US on October 24, landing at Newark International Airport.
Officials say she had a minor fever, necessitating a quarantine at a Newark, New Jersey, hospital.
Kaci Hickox contested the quarantine regimen, ultimately threatening legal action.
After showing no fever or other symptoms for a 24-hour period, Kaci Hickox was discharged and brought to her home state of Maine.
“I’m not willing to stand here and let my civil rights be violated when it’s not science-based,” she told reporters on Wednesday evening.
On Thursday morning, Kaci Hickox left her home on a bicycle, followed by police officers who monitoring her movements and public interactions. She returned home shortly after.
Without a court order, the police were barred from detaining her.
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