A health worker removes items at an apartment complex on Wednesday in Dallas, home to a second nurse in Texas who has tested positive for the Ebola virus. MIKE STONE /GETTY IMAGES/AFP

A second nurse from Texas who has contracted Ebola told a US health official she had a slight fever and was allowed to board a plane from Ohio to Texas, intensifying concerns about the United States' response to the deadly virus.

The nurse, Amber Vinson, 29, flew from Cleveland to Dallas on Monday, the day before she was diagnosed with Ebola, the US Centers for Disease Control and Prevention said.

Vinson told the CDC her temperature was 37.5 C. Since this is below the CDC's temperature threshold of 38 C she was not barred from flying, a source said.

The chances that other passengers were infected were very low because Vinson did not vomit on the flight and was not bleeding, but she should not have been aboard, CDC Director Thomas Frieden said.

Vinson was isolated immediately after reporting a fever on Tuesday, officials at the Texas Department of State Health Services said.

She had treated Liberian patient Thomas Eric Duncan, who died of Ebola on Oct 8 and was the first patient diagnosed with the virus in the US.

Vinson was transferred to Emory University Hospital in Atlanta by air ambulance and is being treated in a special isolation unit. Three other people have been treated there and two have been discharged, the hospital said in a statement.

Television images showed Vinson walking from an ambulance to an Emory hospital door with an escort, both of them in protective clothing.

Vinson, a worker at Texas Health Presbyterian Hospital in Dallas, took a Frontier Airlines flight to Cleveland from Dallas/Fort Worth International Airport on Friday.

She returned to Dallas on Monday aboard another Frontier flight. The CDC said it is asking the more than 130 passengers on this flight to call a hotline.

Frontier Airlines CEO David Siegel said in a letter to employees that the CDC notified the airline on Wednesday morning that Vinson had tested positive for Ebola, then later said she may have been symptomatic while on board the flight.

Frontier took the plane out of service on Wednesday morning for cleaning and put two pilots and four flight attendants on paid 21-day leave as a precaution, the letter said, even though CDC guidance stated the crews were safe to fly.

Between the initial flight on Friday and Wednesday, the plane made at least five more flights, according to the letter.

REUTERS—AP