A doctor who became New York City's first Ebola patient was praised for getting treatment immediately upon showing symptoms, and health officials stressed that the nation's most populous city need not fear his wide-ranging travel in the days before his illness began.

Mayor Bill de Blasio and Gov. Andrew Cuomo urged residents not to be alarmed by the doctor's diagnosis Thursday, even as they described him riding the subway, taking a cab and bowling since returning to New York from Guinea a week ago. 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," 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 Thursday morning coming down with a 103-degree fever and diarrhea. He was being treated in an isolation ward at Manhattan's Bellevue Hospital, a designated Ebola center.

The Centers 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 Cuomo and 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 Spencer's contacts to identify anyone who may be at risk. The city's health commissioner, Mary Bassett, said 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, which is spread through direct contact with the bodily fluids of an infected person, are slim. Someone can't be infected just by being near someone who is sick with Ebola. Someone isn't contagious unless he is sick.

Bassett said the probability was "close to nil" that Spencer's subway rides would pose a risk. Still, the bowling alley was closed as a precaution, and Spencer's Harlem apartment was cordoned off. The Department of Health was on site across the street from the apartment building Thursday night, giving out information to area residents.

Still, the news rankled some New Yorkers. "Oh my gosh!" said Charles Kerr, 60, as his friends gathered on a Harlem sidewalk murmured. "This changes the situation. The guy must be coughing, sitting against people. Now you've got to think."

Kerr said he wasn't afraid, but he wants a stricter approach to anyone coming from the Ebola-affected countries.

"Stay in their apartment," he said. "Especially now, when it's so rampant. Especially if they know they've been in contact."