But the unidentified worker has been unable to pinpoint where that breach might have occurred, according to Dr. Tom Frieden, head of the Centers for Disease Control and Prevention.
"A single inadvertent slip can result in contamination," he said during a briefing, adding that the CDC has recommended that the hospital where the worker is being treated – and where Duncan died Wednesday – should keep "to an absolute minimum" those who care for Ebola patients and should perform only those procedures that are essential to a patient's treatment.
A Texas health care worker who provided hospital care for an Ebola patient who later died has tested positive for the virus, health officials said Sunday in a statement.
Dr. Dan Varga, of Texas Health Presbyterian Hospital, said at a news conference Sunday morning that the worker and his family have requested privacy, and that his condition is stable.
Varga also said the hospital would continue to care for its current patients but will be accepting no new ones. In addition, all staff members are being monitored for the virus.
The health care worker's diagnosis represents the first known case of the disease being contracted or transmitted in the U.S.
A statement posted on the Texas Department of State Health Service's website said "confirmatory testing will be conducted by the Centers for Disease Control and Prevention in Atlanta."
Officials said the health care worker reported a low-grade fever Friday night and was isolated and referred for testing. Preliminary test results were received late Saturday.
Hospital and state health officials did not identify the health care worker or provide their job description.
"We knew a second case could be a reality, and we've been preparing for this possibility," said Dr. David Lakey, commissioner of the Texas Department of State Health Services. "We are broadening our team in Dallas and working with extreme diligence to prevent further spread."
Health officials have interviewed the patient and are identifying any contacts or potential exposures. They said people who had contact with the health care worker after symptoms emerged will be monitored based on the nature of their interactions and the potential they were exposed to the virus.
How Ebola SpreadsAs was stressed at the Sunday news conference, Ebola spreads through close contact with a symptomatic person's bodily fluids, such as blood, sweat, vomit, feces, urine, saliva or semen. Those fluids must have an entry point, like a cut or scrape or someone touching the nose, mouth or eyes with contaminated hands, or being splashed.
The World Health Organization says blood, feces and vomit are the most infectious fluids, while the virus is found in saliva mostly once patients are severely ill and the whole live virus has never been culled from sweat.
Thomas Eric Duncan, the first person diagnosed with Ebola in the U.S., died Wednesday in Dallas. Duncan, 42, grew up next to a leper colony in Liberia and fled years of war before later returning to his country to find it ravaged by the disease that ultimately took his life.
Duncan arrived in Dallas in late September, realizing a long-held ambition to join relatives. He came to attend the high-school graduation of his son, who was born in a refugee camp in Ivory Coast and was brought to the U.S. as a toddler when the boy's mother successfully applied for resettlement.
The trip was the culmination of decades of effort, friends and family members said. But when Duncan arrived in Dallas, though he showed no symptoms, he had already been exposed to Ebola. His neighbors in Liberia believe Duncan became infected when he helped a pregnant neighbor who later died from it. It was unclear if he knew about her diagnosis before traveling.
Duncan had arrived at a friend's Dallas apartment on Sept. 20 — less than a week after helping his sick neighbor. For the nine days before he was taken to a hospital in an ambulance, Duncan shared the apartment with several people.
For more information on Ebola, go to www.cdc.gov/vhf/ebola/.
With additional reporting by STEPHEN M. SILVERMAN