After New York City doctor Craig Spencer tested positive for the Ebola virus Thursday, three people in his circle have been quarantined for possible symptoms. Spencer, who returned to the city after treating Ebola patients in West Africa, travelled widely across New York before his symptoms began, but health officials have said that the city need not fear an outbreak.

According to Mary Bassett, New York City’s health commissioner, the people who have been quarantined are Spencer's fiancée and two of his friends, the Associated Press reported, adding that none of them have so far shown any symptoms. Spencer, 33, is being treated in an isolation ward at Manhattan's Bellevue Hospital, a designated Ebola center, and health officials have been tracing his contacts to identify anyone else who could be at risk of contracting the Ebola virus.

The New York-Presbyterian/Columbia University Medical Center, where Spencer works, said in a statement that he had not seen any patients or been to the hospital since his return from Guinea. The hospital praised him as a “dedicated humanitarian” who “went to an area of medical crisis to help a desperately underserved population.”

Meanwhile, officials have said that the chances of the average New Yorker contracting Ebola are slim. The virus spreads through direct contact with the bodily fluids of an infected person, so people cannot be infected simply by being near someone who has Ebola, according to officials.

Other cases in the U.S. besides Spencer include four American health workers, three of them doctors. The epidemic has killed nearly 4,900 people, mostly in West Africa, where more than 440 health workers have contracted the virus and about half have died from it, AP reported.