15 October 2014 Last updated at 16:21 GMT
US health 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, fell ill on Wednesday.
Both she and Nina Pham, 26, had treated Liberian Thomas Eric Duncan, who died on 8 October, 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 Wednesday, the US Centers for Disease Control and Prevention (CDC) said it wanted to interview the people who flew on Frontier Airlines flight 1143 from Cleveland, Ohio, to Dallas, Texas on 13 October.
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 nurse, who has yet to be identified, was not showing symptoms of the disease when she flew, the crew has told CDC investigators.
Health experts say people who are not showing symptoms are not contagious.
On 14 October, the nurse came down with a fever and was isolated within 90 minutes. Her diagnosis was announced early on Wednesday.
Both the nurse and Ms Pham treated Mr Duncan at Texas Health Presbyterian Hospital in Dallas.
Mr Duncan, who was the first person to be diagnosed in the US with Ebola, started showing symptoms of the disease just days after he arrived in Texas from Liberia, where he contracted the disease.
The World Health Organization (WHO) says 4,447 people have died from the outbreak, mainly in West Africa.
Sierra Leone, Liberia and Guinea have been hardest hit by the outbreak, which began in December 2013 but was confirmed in March.
The second nurse had flown to Cleveland on 10 October, two days after Duncan died, then returned three days later on Frontier Airlines.
In a statement, the airline said the plane “remained overnight at [Dallas] airport… at which point the aircraft received a thorough cleaning per our normal procedures which is consistent with CDC guidelines prior to returning to service the next day. ”
“It was also cleaned again in Cleveland last night,” the airline said.