Athletes staying at one of the team hotels for the World Championships in London have gastroenteritis, event organisers have confirmed.
Public Health England say 30 athletes and support staff have been affected.
Botswana’s Isaac Makwala, who is among the favourites for the 400m, withdrew from Monday’s 200m heats after suffering from the illness.
Several German and Canadian athletes staying at the Tower Hotel fell ill last week.
A further 30 Germans due to arrive on Tuesday will be moved to other hotels.
German triple jumper Neele Eckhardt collapsed but was well enough to compete on Saturday, and took part in Monday’s final.
The Ireland team, who are also staying at the hotel, have confirmed that one athlete – 400m hurdler Thomas Barr – has been affected.
Hotel ‘not the source of the illness’
A Local Organising Committee (LOC) statement said: “There have been a number of cases of gastroenteritis reported by team members residing within one of the official team hotels.
“Those affected have been supported by both team and LOC medical staff. In addition we have been working with Public Health England to ensure the situation is managed and contained.
“As a result, further advice and guidelines have been issued to team doctors and support staff.”
The Tower Hotel said investigations conducted with environmental health officers and the International Association of Athletics Federations (IAAF) had shown the hotel was “not the source of the illness”. That has also been confirmed by Public Health England.
The hotel added: “We have followed strict hygiene protocol, ensuring that those affected are not in contact with other guests and all public areas have been thoroughly sanitised.”
Makwala withdrew ‘on instruction of IAAF’
Makwala, 30, was one of the favourites for the 200m and, without a valid reason for withdrawing, he could have been disqualified from the 400m.
It is unclear whether he will be able to race in the 400m final, which takes place on Tuesday (21:50 BST).
Makwala is considered to be the main challenger to Olympic champion and world record holder Wayde van Niekerk.
The IAAF said Makwala withdrew from the 200m “due to a medical condition on the instruction of the IAAF medical delegate”.