(CNN) -- Concerns about even remote chances of Ebola exposure rippled from a U.S. airline to a ship off Belize on Friday, with Frontier Airlines trying to contact hundreds more passengers of a plane linked to an infected nurse, and a cruise liner quarantining a health worker only tangentially linked to the care of a different Dallas Ebola patient.
The airline's move relates to Amber Vinson, a Dallas nurse who treated an Ebola patient and then was diagnosed with the virus herself this week after taking a round trip between Dallas and Cleveland. On Thursday, a Centers for Disease Control and Prevention official said she could have had symptoms earlier than believed -- a time period possibly covering her two flights on Frontier Airlines.
Frontier now says it is notifying up to 800 passengers total, a figure that includes those on her October 10 Dallas-to-Cleveland flight, the return flight on Monday, plus five other trips taken by the plane before the airline took it out of service. Frontier says it's telling those passengers to contact the CDC -- which had said the risk to anyone on the return flight was extremely low -- if they have any concerns.
The CDC, meanwhile, said it is asking only the passengers on Vinson's two flights to contact it. The CDC said it will interview passengers, answer their questions and monitor anyone determined to be at potential risk.
Vinson is one of two nurses who became ill with Ebola after treating Thomas Eric Duncan at Dallas' Texas Health Presbyterian Hospital. Duncan, a Liberian man who was the first person diagnosed with Ebola in the United States, died earlier this month, and the two nurses -- Vinson and Nina Pham -- are receiving care.
Vinson was hospitalized at the Dallas hospital Tuesday, one day after her return flight from Ohio, where she was visiting family and planning her wedding. Authorities initially said 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.
This is significant because a person isn't contagious with Ebola, which spreads through the transmission of bodily fluids, until he or she has symptoms of the disease.
But on Thursday, Dr. Chris Braden of the CDC told reporters in Ohio that "we have started to look at the possibility that she had symptoms going back as far as Saturday. ... We can't rule out (that) she might have had the start of her illness on Friday."
"So this new information now is saying we need to go back now to the flight that she took on Friday the 10th and include them in our investigation of contacts," he said.
The airline's attempts to contact passengers came as knowledgeable sources told CNN on Friday that President Barack Obama, whose administration has been criticized for its response to U.S. Ebola incidents, will appoint Ron Klain as his "Ebola czar." Klain is a former chief of staff to Vice Presidents Joe Biden and Al Gore.
The few Ebola cases that the United States has seen stem from a months-long outbreak in West Africa, where most of the roughly 9,200 reported Ebola cases and 4,555 deaths have occurred, according to the World Health Organization.
Quarantine on ship off Belize
Meanwhile, a different Dallas hospital worker who may have handled 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.
CDC on Frontier passengers: 'Extremely low' risk
As for Vinson, her uncle Lawrence Vinson said Thursday night that his niece didn't feel sick until after her trip Tuesday morning, when she went to the Dallas hospital with a temperature of 100.3 degrees, which is still below the CDC's Ebola threshold.
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 the agency said it 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, the assistant health commissioner of Summit County, Ohio, which includes Akron, where Vinson was during her trip. The quarantined people include at least two 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
After initial treatment in Dallas, 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.
The other Dallas nurse, Pham, is undergoing treatment at a National Institutes of Health hospital in Bethesda, Maryland. She was transferred there from a Dallas hospital Thursday night.
She is in fair condition, and "she is stable and ... resting comfortably," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said Friday, adding that she is still very fatigued. Fauci said he couldn't detail exactly why she's described in fair condition, citing patient confidentiality.
She is interacting freely with hospital caregivers and is eating, Dr. Richard Davey of the National Institutes of Health told reporters in Maryland.
"We fully intend to have this patient walk out of this hospital, and we will do everything we possibly can to have that happen," Fauci said outside the NIH hospital where Pham is receiving care.
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 cleared 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.
Another Ebola patient, freelance NBC cameraman Ashoka Mukpo, who was flown to Nebraska for treatment after contracting Ebola in West Africa, is "getting better every day" at Nebraska Medical Center, hospital spokesman Taylor Wilson said Thursday.
CNN's Carma Hassan, Gabe LaMonica and Susan Candiotti contributed to this report.