Investigations are under way at a hospital in Madrid after a Spanish nurse became the first person known to have contracted the deadly Ebola virus outside West Africa.
The nurse had treated two Spanish missionaries who died of the disease after being flown home from the region.
Meanwhile, US President Barack Obama has announced plans to screen passengers flying to the United States.
Some 3,400 people have died in the outbreak – mostly in West Africa.
The Spanish auxiliary nurse, a 40-year-old woman whose identity has not been revealed, was one of some 30 staff at the Carlos III hospital in Madrid who had been treating Spanish priests Manuel Garcia Viejo and Miguel Pajares, officials say.
Mr Garcia Viejo, 69, died at the hospital on 25 September after catching Ebola in Sierra Leone.
Miguel Pajares, 75, died in August after contracting the virus in Liberia.
The nurse had twice gone into the room where Mr Garcia Viejo had been treated, before and after his death on 25 September.
Shortly afterwards she had gone on holiday, a hospital spokesman said, but fell ill with fever symptoms on 30 September and was admitted to Alcorcon hospital in south-west Madrid on Sunday after being positively tested for Ebola.
In the early hours of Tuesday she was moved under a police escort to Carlos III hospital in the capital and is said to be in a stable condition.
Her husband and the other members of the medical team are being monitored. It was not known where she had gone on holiday.
It is unclear how the auxiliary nurse could have contracted Ebola.
The hospital was reported to have had extreme protective measures in place including two sets of overalls, gloves and goggles.
However, health workers told El Pais newspaper that the clothing used during the treatment of the two priests did not have level-four biological security, which is fully waterproof and with independent breathing apparatus.
Instead it was level two, the paper says, as photographs provided by staff indicated that the overalls worn did not allow for ventilation and the gloves were made of latex and bound with adhesive tape.
