Residents have been urged to remain calm after a New York doctor, who had recently travelled to Guinea, tested positive for Ebola.
The doctor, who is New York’s first Ebola patient, has been praised for getting treatment immediately upon showing symptoms.
Mayor Bill de Blasio and Governor Andrew Cuomo urged residents not to be alarmed by the doctor’s diagnosis, even as they described him riding the subway, taking a taxi and bowling since returning to New York from Guinea a week ago.
Mr de Blasio said all city officials followed “clear and strong” protocols in their handling and treatment of him.
“We want to state at the outset that New Yorkers have no reason to be alarmed,” Mr de Blasio said. “New Yorkers who have not been exposed are not at all at risk.”
The doctor, Craig Spencer, a member of Doctors Without Borders, reported coming down with a fever. He was being treated in an isolation ward at Manhattan’s Bellevue Hospital, a designated Ebola centre.
The Centres for Disease Control and Prevention, which will do a further test to confirm the initial results, has dispatched an Ebola response team to New York.
President Barack Obama spoke to Mr Cuomo and Mr de Blasio on Thursday night and offered the federal government’s support. He asked them to stay in close touch with Ron Klain, his Ebola czar, and public health officials in Washington.
Health officials have been tracing Mr Spencer’s contacts to identify anyone who may be at risk. The city’s health commissioner, Mary Bassett, said Mr Spencer’s fiancee and two friends had been quarantined but showed no symptoms.
Health officials say the chances of the average New Yorker contracting Ebola, spread through direct contact with the bodily fluids of an infected person, are slim.
Ms Bassett said the probability was “close to nil” that Mr Spencer’s subway rides would pose a risk. Still, the bowling alley was closed as a precaution, and his Harlem apartment was cordoned off.
The department of health was across the street from the apartment on Thursday night, giving information to area residents.
Still, the news rankled some New Yorkers. Charles Kerr, 60, said “This changes the situation. The guy must be coughing, sitting against people. Now you’ve got to think.”
Mr Kerr said he was not afraid, but he wants a stricter approach to anyone coming from the Ebola-affected countries.
Other neighbours expressed concern for the doctor’s health.
“I feel sorry. I just hope they can ... find something to cure it because this is terrible,” said Joyce Harrison.
The epidemic in West Africa has killed about 4,800 people. In the United States, the first person diagnosed with the disease was a Liberian man, who fell ill days after arriving in Dallas and later died, becoming the only fatality.
None of his relatives who had contact with him got sick. Two nurses who treated him were infected and are in hospital. The family of one nurse said doctors no longer could detect Ebola in her as of Tuesday evening.
According to a rough timeline provided by city officials, in the days before Mr Spencer fell ill, he went on a three-mile jog, went to the High Line park, rode the subway and, on Wednesday night, got a taxi to a Brooklyn bowling alley.
He started feeling tired on Tuesday, and felt worse on Thursday when he and his fiancee made a joint call to authorities to detail his symptoms and his travels. Medics in full Ebola gear arrived and took him to Bellevue in an ambulance surrounded by police cars.
Doctors Without Borders, an international humanitarian organisation, said per the guidelines it provides its staff members on their return from Ebola assignments, “the individual engaged in regular health monitoring and reported this development immediately”.
Travellers from Guinea, Liberia and Sierra Leone must report in with health officials daily and take their temperature twice a day, as Mr Spencer did. He also limited his direct contact with people, health officials said.
Mr Spencer, 33, works at New York-Presbyterian/Columbia University Medical Centre. He had not seen any patients or been to the hospital since his return, the hospital said in a statement, calling him a “dedicated humanitarian” who “went to an area of medical crisis to help a desperately under-served population”.
Four American aid workers, including three doctors, were infected with Ebola while working in Africa and were transferred to the US for treatment in recent months. All recovered. Health care workers are vulnerable because of close contact with patients when they are their sickest and most contagious.
In West Africa this year, more than 440 health workers have contracted Ebola and about half have died. But the Ebola virus is not very hardy. The CDC says bleach and other hospital disinfectants kill it. Dried virus on surfaces survives only for several hours.