Ana Mato, Spain's health minister, said the nurse was part of a medical team that treated Manuel Garcia Viejo, a 69-year-old Spanish priest who died last month in Spain after contracting the virus while working in Sierra Leone.
"Two tests were done and the two were positive," a spokesman for the health department of Madrid told the AFP news agency on Monday. The nurse was now in isolation in a hospital on the outskirts of Madrid.
Journalist Miguel Anxo said that the most of the health minister's press conference on Monday was decoted "to trying to calm fears that the disease will spread."
According to Anxo, although the nurse interacted with people freely before being aware of having the disease, "doctors have been clear that until you show symptoms of Ebola, it is supposed not to be contagious, and therefore the authorities are hoping the virus have not spread due to the short span of time since she has displayed symptoms."
The Ebola outbreak in West Africa has killed at least 3,439 people since it began in March, out of nearly 7,500 confirmed, probable and suspected cases. Liberia, Sierra Leone and Guinea are the worst-hit countries.