Mayor Bill de Blasio continued to reassure New Yorkers who may be alarmed after Thursday's news of Dr. Craig Spencer's positive Ebola test at Bellevue Hospital in Manhattan.

"I want to repeat what I said yesterday: There is no cause for alarm," the mayor said at a Friday afternoon news conference.

Spencer is currently hospitalized at Bellevue Hospital, where he is in stable condition, officials said Friday. Three people -- his live-in fiancee and two friends -- are under quarantine and are being monitored.

"The situation is being handled and handled well. Ebola is extremely hard disease to contract. It requires direct contact of blood and bodily fluids. It cannot transmitted through casual contact," he said."We have the finest public health system in this country . . . It is ready for extraordinary challenges. We are fully ready to handle Ebola," de Blasio said.

Spencer, 33, of West Harlem, was put into isolation after he reported having a 100.3-degree fever and gastrointestinal symptoms early Thursday.

Although the doctor rode the subway and hung out in Williamsburg after he returned from his humanitarian mission last week, the elected officials said there are no immediate signs that anyone else has gotten sick. 

“Being in the same subway car or living close to someone with Ebola doesn’t put someone at risk,” the mayor said.

Spencer visited The Gutter in Williamsburg, which has been assessed by the Health Department and deemed safe. He was at Blue Bottle at the High Line, which has also been cleared. The Meatball Shop, where Spencer ate before reporting symptoms, is being assessed and, if cleared, will reopen at 6 p.m. Friday.

New York City Health Commissioner Dr. Mary Bassett said they are tracking Spencer's movements "in an abundance of caution."

Spencer's Hamilton Heights apartment has been sealed off, although the building is still open. Investigators are cleaning and examining the apartment.

"This is a public health crisis," de Blasio said, adding that they expect anyone affected to cooperate with officials.

De Blasio urged any New Yorkers who experience Ebola symptoms and have recently visited one of the three West African countries affected should immediately go to the emergency room or call 911.

He also urged all New Yorkers to get a flu shot.

Spencer, who is an emergency physician with New York-Presbyterian Hospital/Columbia University Medical Center, only began experiencing the symptoms on Thursday morning and immediately called his superiors at Doctors Without Borders, who then notified the city’s Health Department. He was taken by ambulance by a specially trained team in protective suits and had a police escort, officials said.

Doctors Without Borders said in a statement Friday that "a thorough investigation is underway" to determine how Spencer was infected with the virus when he was working for the humanitarian group in Guinea.

In a statement, NewYork-Presbyterian said the doctor "has not been to work at our hospital and has not seen any patients at our hospital since his return from overseas."

He is "a dedicated humanitarian on the staff . . . who went to an area of medical crisis to help a desperately underserved population," the hospital said. "He is a committed and responsible physician who always puts his patients first. . . . Our thoughts are with him, and we wish him all the best at this time."