The Centers for Disease Control and Prevention (CDC) officials are seeking 132 people who flew on a plane with a Texas nurse on the day before she came down with symptoms of Ebola.
The nurse, the second person to catch Ebola in the US, became ill on October 14.
Both she and nurse Nina Pham, 26, had treated Liberian Thomas Eric Duncan, who died on October 8, in Dallas.
Meanwhile, the UN’s Ebola mission chief says the world is falling behind in the race to contain the virus, which has killed more than 4,000 in West Africa.
On October 15, the CDC said it wanted to interview the passengers on Frontier Airlines flight 1143 from Cleveland, Ohio, to Dallas, Texas on October 13.
It said it was taking the measure “because of the proximity in time between the evening flight and first report of illness the following morning”.
The CDC officials are seeking 132 people who flew on a plane with a Texas nurse on the day before she came down with symptoms of Ebola
Both the newly diagnosed nurse, who has yet to be identified, and Nina Pham treated Thomas Eric Duncan early in his stay at Texas Health Presbyterian Hospital in Dallas when he had “extensive production of body fluids”, CDC director Tom Frieden told reporters on Wednesday.
The second nurse flew to Cleveland on 10 October, even though she had had “extensive contact” with Thomas Eric Duncan and was being monitored for signs of Ebola and therefore should not have flown on a commercial aeroplane, Dr. Tom Frieden said.
Nina Pham subsequently became ill and was diagnosed with Ebola. When the second nurse returned from Ohio on Monday evening, she was not showing symptoms of the disease, the crew has told CDC investigators.
Health experts say people who are not showing symptoms are not contagious.
“We will from this moment forward ensure that no other individual who is being monitored for exposure undergoes travel in any way other than controlled movement,” Dr. Tom Frieden said, meaning, for example, in chartered flights or ambulances.
On the morning of October 14, the second nurse came down with a fever and was isolated within 90 minutes. Her diagnosis was announced early on October 15.
One of the ill women is to be transferred to Emory University hospital in Atlanta, which oversaw the recovery of two US aid workers who had caught the disease in Africa.
Dr. Tom Frieden, head of the Centers for Disease Control and Prevention (CDC), has said a mistake was “clearly” made by staff treating Thomas Eric Duncan who died of Ebola in Texas, resulting in one being infected.
The female health worker infected is in an isolation ward in stable condition, awaiting confirmation of her diagnosis.
Tom Frieden said a full inquiry would be made into how the transmission occurred.
He said 48 other people who may also have had contact were being observed.
The health worker at Texas Health Presbyterian Hospital wore full protective gear while treating Ebola victim Thomas Eric Duncan, health officials in Dallas say.
Thomas Eric Duncan, who caught the virus in his native Liberia, died on October 8.
The current Ebola outbreak, concentrated in Liberia, Guinea and Sierra Leone, has resulted in more than 8,300 confirmed and suspected cases, and at least 4,033 deaths.
Dr. Thomas Frieden said a full investigation would be conducted into how the infection had occurred.
A female health worker at Texas Health Presbyterian Hospital has been infected with Ebola virus after treating Thomas Eric Duncan
“Clearly there was a breach in protocol,” he told CBS.
The CDC investigation, he told reporters, would focus on possible breaches made during two “high-risk procedures”, dialysis and respiratory intubation.
Education and training of health workers would be stepped up, he said, and efforts would be made to reduce the number of staff treating Ebola cases.
Dr. Daniel Varga, of the Texas Health Resource, said the health worker had worn a gown, gloves, mask and shield when providing care to Thomas Eric Duncan during his second and final hospital admission.
Following a positive preliminary test for Ebola, follow-up tests on the infected health worker are due to be completed on Sunday, October 12.
Police are guarding the apartment complex where the woman lives in Dallas as decontamination work is carried out.
No details of her identity or position at the hospital have been given, in accordance with family wishes.
Thomas Eric Duncan tested positive in Dallas on September 30, 10 days after arriving on a flight from Monrovia via Brussels.
He had become ill a few days after arriving in the US, and went to the hospital in Dallas with a high fever.
However, despite telling medical staff he had been in Liberia, Thomas Eric Duncan was sent home with painkillers and antibiotics.
Thomas Eric Duncan was later put into an isolation unit at the hospital but died despite being given an experimental drug.