By the time the patient, Dr. Craig Spencer, an emergency doctor who had recently returned from Guinea, arrived at Bellevue Hospital Center in Manhattan by ambulance on Thursday, he was seriously ill, officials said.
Dr. Spencer complicated the tracing process when he told health officials that just the night before, he had gone bowling in Brooklyn, making the long trip there from his home in Upper Manhattan by subway and then returning in a car hired via the taxi service Uber.
City health officials were suddenly faced with the challenge of finding the right balance between trying to find everyone who might have been exposed and responding to a disease that is transmitted only through direct exposure to bodily fluids.