Double 400m world champion Wayde van Niekerk says he wanted to embrace Isaac Makwala when his rival was ordered out of the world championships because of an infectious illness.

The Botswana star, considered Van Niekerk's biggest threat to his 400m/200m double attempt in London, was quarantined until yesterday afternoon amid fears over an outbreak of norovirus (a vomiting bug).

Makwala missed the 200m heats on Monday as well as the 400m final, being turned away at the stadium gate on Tuesday afternoon as organisers moved to prevent the bug from spreading.

"I saw him just before the 200m heats and the only thing I could think of was just wrapping my arms around him and telling him that he should get well soon because I wouldn't want that for any competitor," Van Niekerk said after retaining his 400m crown in 43.98sec.

There had initially been rumours that food poisoning was behind the illnesses, but organisers said the hotel where the outbreak occurred had been cleared.

"There's a lot of fingers that's being pointed right now," Van Niekerk told journalists.

"I really wish that I could even give him my [400m] medal, to be honest with you, but this is sport, these things happen."

Makwala, arguably a bigger danger in the 200m, was given a late backdoor pass into the 200m, being told to compete in a time trial which he passed in the evening before the semifinals where came second.

Van Niekerk sneaked into the final as the fastest loser and at least the SA champion has a chance to test himself against Makwala.

Akani Simbine, however, will miss the final after he came seventh in his semifinal heat last night.