(CNN) -- A Texas hospital health worker who may have handled Thomas Eric Duncan's fluid samples has been quarantined on a cruise ship in Belize -- another reminder of the widespread fears of the deadly virus.
Though the employee did not have direct contact with Duncan, he or she "may have had contact with his specimen," the U.S. State Department said Friday.
A doctor at the cruise ship has declared the worker symptom-free and in good health, but the worker will remain under isolation as a precaution, it said.
It's been 19 days since the worker handled Duncan's fluid samples -- two days shy of the 21-day incubation period for Ebola.
The Texas Health Presbyterian Hospital worker boarded the commercial cruise ship Sunday from Galveston, Texas.
At the time, the Centers for Disease Control and Prevention had not updated its monitoring requirements, and required only self-monitoring, said Jen Psaki, a spokeswoman for the State Department.
"The hospital employee and traveling partner have voluntarily remained isolated in a cabin," Psaki said. "We are working with the cruise line to safely bring them back to the United States out of an abundance of caution."
The Belize government turned down a request by the United States to evacuate the worker through the international airport in Belize City.
"We remain in close contact with U.S. officials ... we have maintained the position that when even the smallest doubt remains, we will ensure the health and safety of the Belizean people," the government said in a statement.
Duncan, the first person diagnosed with Ebola in the United States, died last week.
Hundreds of passengers notified
In the United States, a nurse infected with Ebola at the same hospital may have had symptoms sooner than originally believed, authorities say, and an airline is notifying up to 800 passengers linked to flights she took between Dallas and Cleveland.
In addition to Amber Vinson's round trip, Frontier Airlines is also reaching out to others who were on five subsequent flights that used the same plane.
Vinson was hospitalized Tuesday, a day after she returned from Cleveland to Dallas aboard a Frontier Airlines flight.
The nurse was also part of a team that treated Duncan.
Frontier says passengers linked to flights she took include those aboard her Dallas-to-Cleveland flight on October 10, a return flight three days later and five later flights that used the same plane.
The expanded efforts came after officials said she may have shown symptoms of the virus four days before authorities first indicated. Ebola is contagious when someone is symptomatic.
At first, authorities indicated Vinson had a slightly elevated temperature of 99.5 degrees Fahrenheit (37.5 Celsius), which was below the fever threshold for Ebola, but didn't show any symptoms of the disease while on her Monday flight.
Did she have symptoms earlier?
But Dr. Chris Braden of the Centers for Disease Control and Prevention took a more cautionary approach Thursday.
"We have started to look at the possibility that she had symptoms going back as far as Saturday," he said. "We can't rule out (that) she might have had the start of her illness on Friday."
Based on the new information, he said, the contacts were expanded to those aboard her flight out of Dallas.
Her uncle, Lawrence Vinson, said Thursday night that his niece didn't feel sick until Tuesday morning, when she went to the hospital with a temperature of 100.3 degrees, which is still below the CDC's Ebola threshold.
'Extremely low' risk
A federal official gave different information to CNN's Elizabeth Cohen, including that Vinson said she felt fatigue, muscle ache and malaise while she was in Ohio. She did not have diarrhea or vomiting while in that state or on the flight home.
Health officials are working from the assumption that Vinson may have been ill longer than originally believed.
The CDC said there's an "extremely low" risk to anyone on Frontier's Cleveland-to-Dallas flight, though his agency was reaching out to all 132 passengers as part of "extra margins of safety." Frontier is also grounding its six crew members for 21 days -- the maximum time between when a person can contract Ebola and show symptoms.
In addition, "12 confirmed contacts of Amber Vinson in Ohio ... are currently under quarantine," said Donna Skoda, Summit County's assistant health commissioner. They include at least two people who worked at a bridal store where the 29-year-old nurse went for her wedding planning.
Anna Younker of Coming Attractions Bridal in Akron said CDC officials visited her and asked questions about Vinson. She said they told her to stay home for a few days and monitor her temperature twice a day. Health officials offered to clean up her shop, and she took them up on the offer so her customers can have peace of mind.
But they assured her that contact with the nurse does not mean she has Ebola.
Other Ebola cases
Vinson was flown to Atlanta's Emory University Hospital, where her uncle said she is "feeling OK."
The hospital treated Americans Kent Brantly and Nancy Writebol, and is also caring for an unnamed person with Ebola who went there on September 9.
Another Ebola patient, freelance NBC cameraman Ashoka Mukpo, is "getting better every day" at Nebraska Medical Center, hospital spokesman Taylor Wilson said Thursday.
Another person with Ebola in the United States, Texas Health Presbyterian Hospital nurse Nina Pham, is undergoing treatment at the National Institutes of Health hospital in Bethesda, Maryland.
An additional 76 workers who cared for Duncan, like Vinson and Pham did, have been asked to regularly take their temperatures to gauge whether they have Ebola.
About 50 people from Texas Health Presbyterian have signed a document legally restricting where they can go and what they can do until they are clear of Ebola, Dallas Mayor Mike Rawlings said Thursday night.
Among other things, they'll be placed on a "Do Not Board list" that would prohibit them from flying commercially like Vinson did.