Of the hotel’s 368 rooms, only 225 will have guests to limit crowding on the property.

Guests and hotel staff no longer interact. For check-in, keys are placed in envelopes on a table. Minibars have been taken out of guest rooms. Housekeeping is an amenity of the past; rooms are provided with extra linens and towels.

Dirty items are collected only after guests, who stay for a minimum of seven days, check out and the room has been fumigated. Beds no longer have decorative pillows, which can spread germs. On every nightstand is not a piece of chocolate from turndown service but a bottle of hand sanitizer.

It has been an adjustment. “One of the hotel’s managers was so upset, because he said, ‘Where are we going to give them coffee?” said Dr. Quigley, now known by Four Seasons staff as Dr. Q. “I said: ‘You’re not. We are going to have to change that behavior.’”

(Coffee makers are placed in every room upon request. The hotel also offers boxed lunches.)

The idea to repurpose the Four Seasons came from the hotel’s owner, Ty Warner. He knew it was going to be difficult. He likened it to opening a new hotel. “My mouth went dry when I got the call,” said Rudy Tauscher, the hotel’s general manager.

Mr. Tauscher knew it was wishful thinking, he said, but he was already fantasizing about giving exhausted medical workers “the most delicious breakfast before their hard day of work, from egg-white omelets to smoked salmon bagels, to fresh fruits and fresh juices.”

That did not happen. Instead, Mr. Tauscher helped a new team, spearheaded by Dr. Quigley, plan the emergency residence in a matter of days. Between March 29 and April 2, the day the hotel reopened (it had closed down for the quarantine on March 20), the team reinvented every process, from where staff members would rest during breaks (about a quarter of them are still working), to how guests would replace lost keys.