The nurse wore a mask, gown, shield and gloves as she helped care for a dying Ebola patient in Texas.
And a day after the Centers for Disease Control and Prevention said she tested positive for Ebola, health officials are still trying to figure out how exactly she caught it.
"Something went wrong, and we need to find out why and what," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
The woman, Nina Pham, took basic precautions while treating Ebola-stricken Liberian national Thomas Eric Duncan at a Dallas hospital. Now she is the first person to have contracted the deadly virus in the United States.
There are few details that are known about what might have gone wrong.
On Monday, Dr. Tom Frieden, director of the CDC, told reporters that it's still unknown how the infection occurred, only that a "breach in protocol" for treating a patient happened.
Frieden said state and federal health officials are re-examining those protocols, including the removal of protective gear after contact with an Ebola patient and if it might be helpful to spray virus-killing solution on workers as they leave an isolation unit. He said Monday that the nurse is "clinically stable."
On Monday, she got a blood transfusion from American Ebola survivor Kent Brantly, according to Jeremy Blume, a spokesman for Samaritan's Purse. Brantly was working for Samaritan's Purse in Liberia when he contracted the virus.
Pham, 26, graduated from Texas Christian University's nursing program in 2010, WFAA reported. According to the website for the American Association of Critical Care Nurses, she received certification in critical care nursing on August 1, less than two months before she began caring for Duncan.
Tom Ha, a family friend, described Pham as a devout Catholic who always "puts other people's interests ahead of her own." It's a philosophy she shares with her family, he told CNN.
"They always helped other people and they take pride in helping other people," he said. "That's what this family's all about."
How did it happen?
On Monday morning, an official with direct knowledge of the Texas nurse's case told CNN that CDC disease detectives interviewed the nurse several times and thought there were "inconsistencies" in the type of personal protective gear she wore and with the process used to put the gear on and remove it.
Frieden has spoken of possible ways she became infected. It could have happened when the nurse removed her protective gear -- a bit of infected bodily fluid somehow touching her -- or it she could have come into contact with infected fluid as Duncan received kidney dialysis or respiratory intubation.
Those procedures were "a desperate measure to try to save his life," Frieden said. "Both of those procedures may spread contaminated materials and are considered high-risk procedures."
He said, "When you have potentially soiled or contaminated gloves or masks or other things, to remove those without any risk of any contaminated material ... touching you and being then on your clothes or face or skin ... is not easy to do right."
Or the problem could have been something else entirely.
Taking extra precautions outside recommended CDC protocols can actually increase the odds of infection, Frieden has said. Caregivers are supposed to double their gloves in some situations, but triple gloving is a violation of CDC protocol because it increases the steps to remove gear and could expose a health care worker for longer than needed.
Other caregivers being monitored
The CDC concedes the Texas nurse's case is worrisome.
"It is possible in the coming days that we will see additional cases of Ebola," Frieden said.
That's because others who provided care to Duncan could have had the same kind of breach as the infected nurse. The CDC is still working to compile a list of health care workers who were involved in Duncan's care from September 28 to October 8, the day he died, an official with direct knowledge of the Texas case told CNN on Monday.
The official added that the health care workers who have been identified will be visited twice daily to be checked for fever, one of the symptoms of Ebola. Those workers had previously been self-monitoring, the official said, because they were not -- before the Texas nurse tested positive -- considered high-risk.
The public areas of the nurse's apartment complex have been decontaminated and her neighbors have been notified. The city of Dallas made a reverse 911 call to residents in the area, telling them about the city's second Ebola case.
"I think it needs to be put into context that ... you can't make an extrapolation that this is now a danger more so to the American people," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
But fear is spreading.
When a passenger on a flight from New York to Los Angeles fell ill Sunday, the biggest concern was Ebola. The plane was taken to a remote gate at Los Angeles International Airport. After a few hours, officials determined the woman did not appear to have Ebola, and other passengers were allowed to leave.
And in Louisiana, Attorney General Buddy Caldwell plans to seek a temporary restraining order to block the disposal of incinerated waste from Duncan's personal items at a Louisiana landfill.
"There are too many unknowns at this point, and it is absurd to transport potentially hazardous Ebola waste across state lines," Caldwell said Sunday.