A physician with Doctors without Borders who recently returned from West Africa is being tested for Ebola at a New York City hospital, health officials said on Thursday, according to Reuters.

The doctor developed a fever and gastrointestinal symptoms, the New York City Department of Health and Mental Hygiene said in a statement quoted by the news agency. Preliminary results of the Ebola testing were expected in the next 12 hours.

The doctor was identified as Craig Spencer, who lives in Manhattan’s Harlem neighborhood, according to New York City Councilman Mark Levine.

“A person in New York City, who recently worked with Doctors Without Borders in one of the Ebola-affected countries in West Africa, notified our office this morning to report having developed a fever,” Doctors Without Borders said in a statement quoted by Reuters.

The doctor reported the fever immediately, and Doctors Without Borders said it immediately notified the city health department.

The patient, who returned to the United States within the past 21 days, is being treated at Bellevue Hospital, the city’s health department said.

Twenty-one days is the maximum incubation period for Ebola.

Spencer’s Facebook page showed a photo of him clad in protective gear. It shows he went to Guinea around September 18 and then to Brussels on October 16.

The health department said it was tracing all of the patient’s contacts to identify anyone who may be at potential risk. It said the patient had been transported by a specially trained unit wearing protective gear.

Fears about the spread of Ebola, which has killed nearly 4,900 people, largely in Liberia, Sierra Leone and Guinea, have mounted since the first person diagnosed with the disease in the United States, a Liberian man who had flown to Texas, was hospitalized in Dallas last month.

The man, Thomas Eric Duncan, died on October 8, and two nurses who treated him became infected with the virus. A task force has been set up following missteps in handling the case.