The World Health Organization said Tuesday that the spread of Ebola in Europe is inevitable after a Spanish nurse became the first person outside West Africa to be infected by the virus. The organization's estimate follows growing fears that the virus, which has so far affected people on three continents, may spread rapidly outside Africa.

Teresa Romero, who contracted Ebola after treating two Spanish missionaries for the virus at the Carlos III hospital in Madrid, is receiving care in the same facility. Rafael Perez-Santamaria, head of the Madrid hospital, said that it is revising its protocols following Romero’s admission with the disease. Four people, including Romero’s husband, are being observed in the hospital, where one tested negative for the virus. Meanwhile, 22 others who came in contact with Romero are being monitored outside the hospital.

WHO’s European director Zsuzsanna Jakab said, according to The Guardian, that it is "quite unavoidable ... that such incidents will happen in the future because of the extensive travel from Europe to the affected countries and the other way around," adding: “The most important thing in our view is that Europe is still at low risk, and that the western part of the European region particularly is the best prepared in the world to respond to viral hemorrhagic fevers including Ebola."

However, several doctors reportedly protested outside the Carlos III hospital demanding to know how Romero became infected, and expressed concern about the hospital's effort to contain the virus' spread.

"Given that both the transmission methods and the methods of prevention are well known, it is clear that some mistake was made," the Madrid College of Doctors said in a statement, according to Reuters.

Jonathan Ball, a professor of molecular virology at Britain's University of Nottingham, said, according to ABC News: "It will be crucial to find out what went wrong in this case so necessary measures can be taken to ensure it doesn't happen again.”

Spanish health officials have reportedly increased safeguards inside hospitals to contain a further spread of the disease, and according to WHO, the chances of a full-scale outbreak in Europe are far-fetched.

Meanwhile, on Monday, scientists said that there was a 75 percent chance that the Ebola virus may reach France by Oct. 24 and a 50 percent chance that it could reach the UK by then.

The latest outbreak of the Ebola virus has killed more than 3,400 people and has infected nearly 7,200 people, mostly in West Africa.