(CNN) -- A nurse with Ebola may have shown symptoms of the virus as many as four days before authorities once indicated, meaning that she might have been contagious while flying on not just one, but two commercial flights, officials said Thursday. Amber Vinson was hospitalized Tuesday, one day after she took a Frontier flight from Cleveland to Dallas. Tests later found that Vinson -- who was among those who cared for Thomas Eric Duncan, the first person diagnosed with Ebola in the United States, at Dallas' Texas Health Presbyterian Hospital -- had Ebola. Authorities indicated Vinson had a slightly elevated temperature of 99.5 degrees Fahrenheit, 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.
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NEW: Nina Pham, a Texas nurse with Ebola, arrives in Maryland for treatment
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NEW: Frontier is notifying up to 800 from multiple flights for possible exposure
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NEW: Amber Vinson's uncle: She wasn't sick until Tuesday, is now "feeling OK"
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An official counters, saying Vinson felt fatigue, muscle ache, malaise in Ohio
The @placeholder hospital said that transferring Nina Pham "is the right decision (because) many of the medical professionals who would normally staff the intensive care unit (are) sidelined for continuous monitoring."