The news comes only days after the U.S. recorded its first case of ebola, albeit in a man who had contracted the virus in his home country of Liberia.

The news sparked the first major reaction on Europe’s financial markets to the ebola outbreak, sending airline stocks plunging as investors priced in a sharp drop in demand by passengers afraid of catching the disease in an aircraft’s closed environment. By lunchtime in Europe, shares in most European airlines were down by between 3.5% and 7%.

The nurse, who has not been identified, was among the staff at the Carlos III hospital in Madrid treating two priests who had been repatriated to Spain after contracting the virus in Sierra Leone. Both subsequently died.

The nurse has herself now been moved into the same hospital and is reported to be in a stable condition. Her husband has also been placed in an isolation ward as a precaution.

It isn’t clear how the disease was transmitted. The BBC quoted Madrid health care director Antonia Alemany as saying that “The nurse went into the room wearing the individual protection gear and there’s no knowledge of an accidental exposure to risk.”

The newspaper El Pais cited staff at the Carlos III hospital as saying that the safety equipment used there didn’t meet the necessary safety standards, which require that clothing and breathing apparatus be fully waterproof. The virus is spread through bodily fluids such as sweat, blood and urine. The hospital deputy director, Yolanda Fuentes, denied the allegations.

Spanish health authorities are trying to track down those with whom she may have been in contact since her exposure to the virus. The woman reportedly went on vacation a day after one of the patients died.

The newspaper El Pais reported that the authorities have already placed under surveillance 22 hospital staff and 30 others known to have had contact with the nurse.

Note: This story has been updated to include financial market reaction to the news.