More than 20 swimmers, including former Olympic champion Liu Zige, were struck down with diarrhoea and fever while competing at the Chinese national championships this week.
The municipal government of Huangshan, the central Chinese city that hosted the five-day swimming championships for the 372 competitors, said they were still unsure what caused the outbreak which was being investigated.
The official Xinhua news agency said Liu, who won the 200 metres butterfly at her home Beijing Games in 2008, and Ning Zetao, who won four golds at the recently concluded Asian Games in Incheon, were among those swimmers hit by the bug.
Ning was forced to withdraw from the 50 metres freestyle on Saturday evening because of the sudden sickness with Youth Olympics champion Yu Hexin taking advantage of his absence to win gold.
Xinhua said the sick athletes had all now recovered and headed home.