Isaac Makwala reacts after winning his 400m heat on Sunday. Photo: Martin Meissner, AP

LONDON – Botswana star Isaac Makwala was withdrawn from the world 400m final on Tuesday after an outbreak of the norovirus bug at a hotel hosting athletes at the IAAF World Championships.

“Isaac Makwala was withdrawn from the men’s 400m (final) due to a medical condition on the instruction of the IAAF medical delegate,” world athletics’ ruling body said in a statement.

Makwala was withdrawn from the first round of the 200m on Monday for the same reason, but insisted on Tuesday he was ready to run the 400m, scheduled for 10.52pm South African time, before the IAAF stepped in.

He has been in top form and would have been one of the main rivals to Olympic champion and favourite Wayde van Niekerk for the gold medal in the final.

Public Health England said 30 athletes and support staff had been affected at a central London hotel, with two cases confirmed as being the norovirus bug.

Dr Deborah Turbitt of Public Health England (PHE) said: “PHE has been notified of a confirmed outbreak of norovirus among people associated with the World Athletics Championships.

“We have so far been made aware of approximately 30 people reporting illness, and two of these cases have been confirmed as norovirus by laboratory testing.

“PHE has been working closely with the London 2017 organisers and the hotel to provide infection control advice to limit the spread of 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.