A Spanish hospital official says the nursing assistant infected with Ebola is "stable," hours after authorities described her condition as critical.

A spokeswoman for the Carlos III hospital in Madrid said the patient, Teresa Romero, remained in serious condition Friday but could give no further details.

She spoke on condition of anonymity in keeping with hospital regulations.

Madrid regional government health chief Javier Rodriquez said Thursday that Romero was in critical condition after taking a turn for the worse.

She is the first person known to have caught the disease outside the outbreak zone in West Africa. She contracted the virus while helping treat a Spanish missionary who became infected in West Africa, and later died.