Several athletes have come down with a stomach bug at the world championships, including medal favorite Isaac Makwala of Botswana.
Makwala pulled out of his 200-meter heat Monday and later said he had food poisoning.
"There have been a number of cases of gastroenteritis reported by team members residing within one of the official team hotels," the local organising committee said in a statement, putting a dampener on the 10-day event. "Those affected have been supported by both team and LOC medical staff."
Makwala wrote on his Facebook page that other athletes were also hit by the bug.
Makwala was expected to be the main challenger to Wayde van Niekerk in both the 200 and the 400. The 400 final is today.
"Let's hope they will allow me to run my final," Makwala wrote.
Van Niekerk certainly wasn't affected by the bug. He easily qualified for the semifinals of the 200 and is the favorite for gold in Usain Bolt's absence.
Although Van Niekerk has a strong chance for double gold, South African teammate Semenya missed out on one yesterday, finishing with bronze in the 1,500 meters.
Semenya had the speed, but left it too late to challenge for the title. She was in 10th place in the 12-woman final going into the last lap and fought back to medal behind Faith Kipyegon of Kenya and Jenny Simpson of the United States.
"A lot cannot go your way in a final, so to come out with a bronze is amazing," Semenya said.
Semenya, a two-time Olympic champion over 800 meters, now must concentrate on her signature event later this week to win another world title, eight years after she won her first at the 2009 Berlin worlds.
Kipyegon took charge in the final straight when the others faltered to give Kenya its second gold and fifth medal overall in the championships.
In the most stirring final of the night, 21-year-old Yulimar Rojas edged Olympic champion Caterine Ibarguen by two centimeters to give Venezuela its first ever world title.
In a seesaw battle, Rojas finally came out on top of her Colombian rival with a mark of 14.91 meters on her penultimate attempt, beating the defending champion's earlier mark of 14.89.
Anyone looking for a feel-good story would gladly have handed the 110-meter hurdles gold medal to Aries Merritt, who had kidney transplant two years ago and was getting back to the form that won him gold in at the 2012 Olympics in the same stadium.
It was not to be.
Running in the outside Lane 9, he finished fifth - well behind Olympic champion Omar McLeod.
"I am back on the world stage, that's the main thing," Merritt said.
McLeod gave Jamaica its first gold of the championships after a disappointing start, when Bolt only got bronze and Elaine Thompson finished outside the medals in the 100 meters.
"It's totally different to last year where we had Usain and Elaine winning, which I used to propel me," McLeod said. "I didn't have that this time so I really wanted to come out and shine my own light."
In the first final yesterday, Anita Wlodarczyk of Poland left it late but won her third world title with one massive hammer throw.
Wlodarczyk, the dominating figure over the past half- decade with two Olympic gold medals, took the lead on her fourth of six attempts and then had her winning throw of 77.90 meters on her penultimate attempt.
Early leader Wang Zheng of China took silver with a throw of 75.98 meters and another Pole, Malwina Kopron, won bronze with a toss of 74.76.
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