Three people associated with the Athletics World Championships have contracted the norovirus with another 40 reporting symptoms, Public Health England (PHE) announced on Thursday.
Isaac Makwala, one of those who was diagnosed with the illness on Monday, runs later on Thursday in the 200 metres final having been allowed to run a solo time-trial on Wednesday.
He had been barred from the heats after being placed under quarantine for 48 hours as is required under British health regulations.
The Botswana runner also missed the 400m final due to being in quarantine.
"PHE has been notified of a confirmed outbreak of norovirus among people associated with the World Athletics Championships," said PHE London deputy director for health protection Dr Deborah Turbitt.
"We have so far been made aware of approximately 40 people reporting illness and three of these cases have been confirmed as norovirus by laboratory testing.
"PHE has been working closely with the London 2017 organisers and venues to provide infection control advice to limit the spread of illness."
London 2017, the championship organisers, announced on Monday several competitors -- staying at the same official team hotel -- had suffered gastroenteritis.
A spokesperson for the Tower Hotel on Tuesday insisted it was "not the source of the illness".
Norovirus is often caught through close contact with someone carrying the virus or by touching contaminated surfaces or objects.
Norovirus, which brings on diarrhoea and vomiting, is rarely serious, with most people making a full recovery within one or two days, without treatment
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