Thomas Frieden, director of the Centers for Disease Control and Prevention, provided an update Monday to the investigation into the spread of the Ebola virus to a nurse at a Dallas hospital. Frieden also apologized for his initial remarks about the nurse’s infection, which some felt blames the nurse or other health-care workers for the infection. (AP)

As a 26-year-old Dallas nurse lay infected in the same hospital where she treated a dying Ebola patient last week, government officials on Monday said the first transmission of the disease in the United States had revealed systemic failures in preparation that must “substantially” change in coming days.

“We have to rethink the way we address Ebola infection control, because even a single infection is unacceptable,” Thomas Frieden, director of the Centers for Disease Control and Prevention, said in a news conference.

Frieden did not detail precisely how the extensive, government-issued safety protocols in place at many facilities might need to change or in what ways hospitals need to ramp up training for front-line doctors or nurses.

But his message was clear: With Ebola, there is no margin for error. The Dallas case made that certain.

Federal, state and local health officials on Monday raced to investigate how Nina Pham, a nurse at Texas Health Presbyterian Hospital in Dallas, became infected with Ebola. A 2010 graduate of Texas Christian University’s nursing program, she was part of the team that treated Thomas Eric Duncan, a Liberian man who succumbed to the virus Wednesday after more than a week at the hospital.

Officials have said Pham wore protective gear, including a gown, gloves, a mask and a face shield, while caring for Duncan on multiple occasions. But Ebola can easily infect those who come into contact with the bodily fluids of Ebola patients, and the smallest slip in putting on or taking off protective gear can open the door to the virus.

Authorities on Monday also were working to determine how many other health-care workers at the hospital could have been exposed to the virus. About 70 staffers cared for Duncan, according to records obtained by the Associated Press.

“We need to consider the possibility that there could be additional cases, particularly among the health-care workers who cared for [Duncan] when he was so ill,” Frieden said. “We would not be surprised if we did see additional cases.”

Asked about how many people at the hospital might be at risk and in need of monitoring, Frieden said: “It’s a relatively large number, we think. . . . We cast a wide net and then narrow that down.”

Pham, whom family members and a church rector identified to a Dallas television station as the infected nurse, remained in stable condition at the hospital Monday, officials said. Investigators had tracked down only one person she might have had contact with since showing symptoms of the disease Friday. Pham, who had been at home taking her temperature twice a day, notified the hospital when she developed a fever, and she quickly was admitted to an isolated unit.

Kent Brantly, a U.S. doctor infected with Ebola this summer while treating patients at a missionary hospital in Liberia, went to the Dallas hospital on Sunday and donated his blood for Pham. The hope is that giving an Ebola victim an injection of blood plasma from a survivor could deliver antibodies that help fight off the virus.

Brantly, who was flown to Atlanta for treatment after his diagnosis and later released, was in Texas at the end of last week to deliver a speech at his alma mater, Abilene Christian University. A spokesman for Samaritan’s Purse, the Christian aid group for which Brantly worked in Africa, said the Dallas hospital got in touch with him after Pham’s diagnosis to see if he would be willing to donate. Brantly made the 180-mile trip east to offer his blood.

The challenge of suiting up for Ebola

It is the third time he has donated blood since recovering from Ebola. He gave blood for another infected American doctor as well as for an Ebola-stricken NBC cameraman, both of whom were treated in Nebraska. Brantly also offered to donate blood to Duncan before his death, but their blood types were not a match.

Meanwhile, the 48 people known to have had possible contact with Duncan before his hospitalization, including 10 “high risk” family members who cared for him or stayed in the same apartment, continue to show no symptoms.

“Everybody’s okay,” said Aaron Yah, who is in quarantine along with other relatives of Duncan. He said that no one, including Duncan’s girlfriend, has shown any signs of infection.

As investigators work to figure out how Pham got infected, health officials already are considering exactly what protocols need strengthening at U.S. hospitals. The CDC said it will examine every aspect of dealing with suspected or confirmed Ebola cases, including how best to staff isolation units and how protective gear is put on and taken off.

“We have not identified a specific problem that led to this infection,” Frieden said. “We have identified a series of things where we can make the care safer and easier for the health-care workers that are providing it.”

Some new measures already are being put in place, Frieden said. Among other things, the CDC says a “buddy system” is essential for health-care workers to ensure the proper removal of protective gear. It is unclear whether that practice was in place in Dallas and how common it is elsewhere.

The chief executive of Texas Health Resources, which operates the Dallas facility, spoke Monday at a town-hall meeting there for hospital employees. “In our collective efforts to improve our knowledge, processes and outcomes, we must not lose sight of the compassion and selflessness a member of our family, and others, have demonstrated to care for others infected with this insidious disease,” CEO Barclay Berdan said. Acknowledging the scrutiny the hospital is under, he added: “We recognize the professional, tireless and compassionate care you provide each and every day. We are staying focused on taking care of our patients and each other.”

In recent days, National Nurses United, the largest union of registered nurses in the United States, has insisted that most hospitals are still not prepared to properly deal with Ebola. Nurses have complained of inadequate training or in some cases almost no training at all on the correct protocols. That lack of preparation is unacceptable, given the risk that front-line health workers face in treating potential Ebola patients, the nurses say.

That sentiment also prompted Frieden to apologize Monday for remarks he made immediately after Pham’s infection was announced. He said over the weekend that “a breach in protocol resulted in this infection,” a remark that some people interpreted as faulting the nurse.

“That was certainly not my intention. People on the front lines are really protecting all of us,” Frieden said. “The enemy here is a virus, Ebola. It’s not a person. It’s not a country. It’s not a place. It’s not a hospital. It’s a virus. It’s a virus that’s tough to fight.”

Yellow police tape on Monday cordoned off the two-story brick apartment building where Pham and her boyfriend live. Sheriff’s deputies and Dallas hazmat units lingered in front of the building for hours. A man in a Dodge truck from Louisiana with the name “OMI Environmental Solutions” on the side arrived about 9 a.m.

Meanwhile, the enhanced screening that began at John F. Kennedy International Airport in New York over the weekend has flagged 91 travelers who came from the three West African countries hardest hit by Ebola. Five people were stopped for additional screening, Frieden said. None had a fever or Ebola.

Similar screening will roll out at airports in Washington, Atlanta, Chicago and Newark later this week.

The White House said Monday that President Obama met with members of his public health and national security team to discuss the situation in Texas. Frieden and Health and Human Services Secretary Sylvia Mathews Burwell detailed the personnel and resources that have been sent to Dallas, as well as various efforts underway to heighten awareness and increase training for health-care workers throughout the country.

As Pham began her fight against the deadly virus in Dallas, the incinerated belongings of the Ebola patient she had treated were bound for a Louisiana hazardous-waste landfill — until the state’s attorney general, Buddy Caldwell, raised concerns that Duncan’s ashes could pose a danger to the state’s population.

Caldwell’s office said in a statement Monday that a Louisiana judge had granted its request for a temporary restraining order blocking the transportation of Duncan’s remains into the state. Despite the CDC guidelines saying that Ebola-related waste that has been incinerated is no longer infectious, Caldwell said that too many questions remain. “Even the CDC and our health-care workers seem uncertain as to the effectiveness of purported protocols in dealing with Ebola,” Caldwell said. “It is absurd to transport potentially hazardous Ebola waste across state lines.”

The order from Judge Bob Downing of Louisiana’s 19th District Court bars the Texas company that destroyed Duncan’s belongings from transporting the ashes into the state. It also prohibits the Louisiana facility slated to accept them from doing so. The order remains in place until Oct. 22, when Downing will hear arguments in the case.

Berman and Dennis reported from Washington. Lena H. Sun, Abby Ohlheiser and Juliet Eilperin contributed to this report.