New York officials said physician Craig Spencer registered a fever for the first time Thursday before officials later determined he had Ebola.
But officials said during a press conference Thursday night they don’t believe Spencer was sick when he rode the subway or went bowling on Wednesday night.
Ebola patients are not contagious when they are asymptomatic.
“There is no reason for New Yorkers to be alarmed,” New York City Mayor Bill de Blasio. “Ebola is an extremely hard disease to contract.”
New York Gov. Andrew Cuomo said city officials have identified four people who came into contact with Spencer after he became sick. Spencer had been checking his temperature twice a day.
Spencer helped Doctors Without Borders in West Africa before flying into New York. The four people are not symptomatic but are being monitored.
Spencer is being treated at Bellevue Hospital in Manhattan. The hospital has been preparing for Ebola patients, officials said and has an isolation unit.
Doctors Without Borders released the following statement:
"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. As per the specific guidelines that Doctors Without Borders provides its staff on their return from Ebola assignments, the individual engaged in regular health monitoring and reported this development immediately. While at this stage there is no confirmation that the individual has contracted Ebola, Doctors Without Borders, in the interest of public safety and in accordance with its protocols, immediately notified the New York City Department of Health & Mental Hygiene, which is directly managing the individual’s care.
"At this stage Doctors Without Borders will not be providing any further details about its colleague."
To date, Thomas Eric Duncan is the lone person in the United States to die of Ebola, while five other patients have successfully been treated in the United States. One other, Dallas nurse Nina Pham is reportedly in good condition.
However, the disease has spread in West Africa. Mali officials confirmed its first case of Ebola after a two-year-old girl tested positive for the disease, according to the BBC.
To find out more about the disease, look at this interactive timeline.