She described the episode as a preview of what may happen in New York State, where more than 170 cases had been confirmed as of Tuesday afternoon.

“You can think of the trickle effect that will have, how that will impact care,” Ms. Edmund-Sealey said. “That’s what will happen now that we’re in crisis.”

This article is based on interviews with several people who work at Lawrence and came into contact with Mr. Garbuz during his stay there. (He was later transferred to a hospital in Manhattan, where he remained on Tuesday.) It will be some time before public health officials determine how many people at the hospital end up being infected.

Regardless, better understanding of what happened over Mr. Garbuz’s four days at Lawrence, which has about 290 beds, could help other hospitals more quickly make diagnoses in the future. It could provide insight into how hospitals might limit the number of people exposed to each patient. In the larger picture, it may help contain the spread of an outbreak.

“He is a very caring hardworking person who constantly cares for his clients and those around him over himself,” Adina Lewis Garbuz, Mr. Garbuz’s wife, said about him on Facebook. Both of them work at a law firm in Manhattan. “I think it is from this that he was run down and susceptible to the illness he acquired. So, I ask all of us who are running on the hamster wheel of life, particularly us New Yorkers, to learn from this and take a moment to take care of yourself.”

An X-ray taken shortly after Mr. Garbuz arrived at Lawrence on Feb. 27 seemed to show he had pneumonia. He was taken to a room on the hospital’s fifth floor, but then was moved to another room. At first, he was walking on his own. But as his breathing troubles worsened, he told hospital workers that he could no longer walk. He was given a wheelchair.

With his health deteriorating, he was moved again, this time to the critical care unit on the third floor. Each of these moves brought him into contact with more staff members and patients.