Doctors treating a Spanish nurse infected with the deadly Ebola virus were cautiously optimistic about her condition on Tuesday after she survived the potentially critical two-week period after being infected.

"She is in stable condition, and this is a good day, the 15th day" since she first showed symptoms of the illness, said Marta Arsuaga, a doctor at the specialist tropical disease hospital Carlos III.

"Statistics show that usually the disease is most deadly up to the 13th or 14th day. Now it is one day after that, so that is good," she told reporters at the hospital.