By Lisa Maria Garza and Terry Wade

DALLAS (Reuters) – A second Texas nurse who has contracted Ebola told a U.S. health official she had a slight fever and was allowed to board a plane from Ohio to Texas, a federal source said on Wednesday, intensifying concerns about the U.S. 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 U.S. Centers for Disease Control and Prevention (CDC) said.

Vinson told the CDC her temperature was 99.5 Fahrenheit. Since that was below the CDC’s temperature threshold of 100.4F “she was not told not to fly,” the source said. The news was first reported by CNN.

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 Dr. Thomas Frieden told reporters.

Congress will hold a hearing on Thursday on the U.S. response to Ebola, with Frieden and other officials scheduled to testify.

Vinson was isolated immediately after reporting a fever on Tuesday, Texas Department of State Health Services officials 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 United States.

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

(Additional reporting by Jim Forsyth in San Antonio, Susan Heavey and Doina Chiacu in Washington and Jon Herskovitz in Austin, Texas; Writing by Jonathan Kaminsky and Curtis Skinner; Editing by Bernadette Baum and Dominic Evans)