(CNN) A Texas doctor has apologized for what he calls mistakes for how his hospital handled Ebola as schools close out of fear that they're vulnerable to the virus. Also on Thursday, officials are considering ordering that 76 hospital workers who treated an Ebola patient be ordered not to board airplanes.

The director of the Centers for Disease Control and Prevention says a second nurse who tested positive for Ebola, who flew a day before it was known that she might be suffering from the virus, should not have been cleared to fly.

She reported to the agency that she had a fever, she said, but was told she could go ahead and continue her travel. Now 132 passengers on her flight are wondering if they were exposed.

As the list of missteps grow, here's the latest on Ebola in the United States:

Hospital official: 'We are deeply sorry'

The Texas hospital where an Ebola patient died and two nurses became infected is apologizing for mistakes made when first confronted with the deadly virus.

Nina Pham, the first nurse infected, will be transferred to a National Institutes of Health facility in Maryland, according to two sources familiar with the situation. She is now being cared for in Dallas at the same hospital where she worked and where she contracted the virus from a patient she treated, Thomas Eric Duncan.

Duncan had traveled from Liberia to Texas in September. He died of the virus at the hospital in early October. "Unfortunately, in our initial treatment of Mr. Duncan, despite our best intentions and a highly skilled medical team, we made mistakes," Varga, the chief clinical officer for Texas Health Services, said in written testimony to the House Energy and Commerce Committee.

"We did not correctly diagnose his symptoms as those of Ebola. We are deeply sorry."

Days after Duncan returned to the hospital, he died from the virus.

But Varga did outline a timeline of the hospital's preparation, saying hospital staffers were given guidance on looking for Ebola symptoms several times over the summer.

He said the hospital has made several policy changes, such as updating the emergency department screening process to include a patient's travel history and increasing training for staffers.

CDC might ground Texas hospital workers

The federal government is weighing putting those who treated Duncan on a list that would prohibit them from being able to fly, an official familiar with the situation told CNN.

The official also said the CDC is considering lowering the fever threshold that would be considered a possible sign of Ebola. The current threshold is 100.4 degrees Fahrenheit.

The idea came after news that Amber Vinson, a nurse who cared for Duncan, flew home from Cleveland to Dallas after reporting a fever.

Vinson called the CDC to report an elevated temperature of 99.5 Fahrenheit. She informed the agency that she was getting on a plane, a federal official told CNN, but she wasn't told to stay grounded.

CDC Director Tom Frieden said Vinson shouldn't have flown because she helped care for Duncan, and because another health worker who cared for him had already been diagnosed with the virus.

He said there's an "extremely low" risk to anyone else on that plane, but the agency is reaching out to everyone on the flight as part of "extra margins of safety."

Vinson, 29, is now being treated at Emory University Hospital in Atlanta, which has successfully treated two other Ebola patients and has not had any employees infected.

Staffing issues at the Texas hospital led to the decision to transfer Vinson to Emory, a federal official told CNN Chief Medical Correspondent Dr. Sanjay Gupta.

"What we're hearing is that they are worried about staffing issues and a possible walkout of nurses," the official said.

Hospital employees can quarantine themselves

With two of its own nurses infected with Ebola, Texas Health Presbyterian said it will allow any concerned employee to have a hospital room.

"Texas Health Dallas is offering a room to any of our impacted employees who would like to stay here to avoid even the remote possibility of any potential exposure to family, friends and the broader public," the hospital said in a statement.

"We are doing this for our employees' peace of mind and comfort. This is not a medical recommendation. We will make available to our employees who treated Mr. Duncan a room in a separate part of the hospital throughout their monitoring period."

Several Texas and Ohio schools close

News of Vinson's travel on a Frontier Airlines plane led to school closures in two states.

In Texas, a few schools in the Belton Independent School District are closed Thursday because two students were on the same flight as Vinson from Cleveland to Dallas -- Frontier Airlines Flight 1143, the superintendent said.

And in Ohio, two schools in the Solon School District in suburban Cleveland are closed Thursday because a staffer "traveled home from Dallas on Frontier Airlines Tuesday on a different flight, but perhaps the same aircraft" as Vinson, the school district said in a statement.

"Although we believe what the science community and public health officials are telling us about the low risk of possible transmission of the virus through indirect contact, we are nonetheless taking the unusual step of closing the dual school building for Thursday so that we can have the schools cleaned and disinfected," the statement said.

Frontier Airlines grounds 6 crew members

The school districts aren't the only ones concerned about Vinson's travels.

Frontier Airlines placed six crew members on paid leave for 21 days "out of an abundance of caution," CEO David Siegel wrote in a letter to employees.

The airline also removed the plane's seat covers and carpet near where the infected passenger sat, even though it had not been asked to by the CDC, Siegel said.

Hospital fires back after claims

After scathing allegations by a nurses' union , a Texas Health Presbyterian spokeswoman said several of the claims were not true.

National Nurses United, citing interviews with nurses at the hospital, said Duncan was "left for several hours, not in isolation, in an area where other patients were present" during his second visit to the hospital.

But hospital spokeswoman Candace White said Duncan "was moved directly to a private room and placed in isolation" during his second visit.

And after the union claimed "there was no one to pick up hazardous waste as it piled to the ceiling," White said the waste was "well-contained in accordance with standards, and it was located in safe and containable locations."