GWANGJU, South Korea -- Katie Ledecky's phone pinged with a middle-of-the-night text from Michael Phelps.
Sick and struggling to fall asleep, she read his message of concern from half a world away.
"What's up? Are you OK?" the 23-time Olympic gold medalist asked.
Ledecky had been confined to her room because of dehydration and vomiting that caused her to withdraw from the 1,500-meter freestyle final and 200 free heats at the world swimming championships.
Having her former teammate check in was just the medicine Ledecky needed.
"That meant a lot," she said Thursday. "That gave me a little bit (extra)."
Ledecky returned to competition in the 4x200 free relay final, her first racing since preliminaries on Monday.
She rallied the U.S. to the lead on her second leg, but the Americans finished second to Australia, which set a world record.
Her coach, Greg Meehan, said Ledecky was cleared by the U.S. medical staff.
"It's a test, honestly," he said. "We're fortunate she's feeling well enough to race."
Meehan said Ledecky's symptoms first began near the end of the U.S. team's training camp in Singapore.
"We don't know exactly what caused this all," she said. "I wouldn't have pulled out if it wasn't serious or if I wasn't concerned and scared and worried about my health. Just kind of created the perfect storm that pulled me out."
Ledecky said she expected to compete in the 800 free heats on Friday.
She was upset in the 400 free final on Sunday, earning a silver medal. She was the defending champion and fastest qualifier in the 1,500 free.
"The fact that she didn't swim the 1,500, where it's a medal for her and it's likely a gold medal if things go well, I think is a good indication that it wasn't about anything other than she was ill," Meehan said.
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