The condition of New York City’s first Ebola patient, Dr. Craig Spencer, worsened over the weekend, though he remained awake and communicative, health officials said.

Dr. Spencer, 33, was “entering the next and more serious phase of his illness, as anticipated with the appearance of gastrointestinal symptoms,” Ana Marengo, a spokeswoman for the city’s public hospital system, said in a statement. Dr. Spencer has been in isolation at Bellevue Hospital Center since Thursday, when he reported having a fever of 100.3 degrees.

The statement was careful not to convey a sense of pessimism, and patients undergoing treatment can worsen before they recover. In a brief telephone interview from his room at Bellevue, Dr. Spencer spoke of his sickness in a neutral tone that seemed stripped of illusions: “I’m still undergoing treatment,” he said.

Dr. Spencer said he had received “about 200 calls from reporters and 300 emails.” Adding that he did not mean to offend, he said, with a touch of wry humor, that he had other priorities: “When you have Ebola, not the best way to spend your time.”