Another day at the gym, her teammate Mikaela Mayer put her shoe on Fuchs. “Ginny freaked all the way out,” Shields said. “She ran to a shower and we didn’t hear from Ginny for a couple hours.”

Mayer, a 2016 Olympian and Fuchs’s best friend, noticed something was amiss the first time they shared a hotel room. Fuchs wouldn’t get out of the bathroom.

“Within two hours, there was no toilet paper, all the towels are on the floor and dirty,” Mayer said. “She didn’t even shower and all the soap was gone. I was like, ‘Are you kidding me?’ I started to spy on her. I would watch her do these routines. I would bust in the door and be like, ‘What did I just see?’”

What people don’t know, Mayer said, is that as soon as Fuchs leaves the gym, she remembers exactly where blood spattered, snot flew and precisely where an armpit touched her shoulder.

“She uses her shower time scrubbing those parts of her body and remembering that,” Mayer said.

Unlike other O.C.D. cases, Fuchs’s cleaning rituals aren’t dictated by a fixed number of repetitions. “It’s a feeling,” she said. “I’m always searching for that perfect clean feeling.”

Yet she is not a neat freak.

Far from it, Mayer said, because Fuchs’s idea of clean is completely different. “To her, it’s not visual; it’s all about germs and contamination,” Mayer explained. “So you’ll walk into her room and there are clothes all over the floor, but it’s a ‘clean’ area.”

Mayer and Koroma are really the only ones who see Fuchs struggle up-close, on a daily basis.