There was no mandatory test upon arrival in Eugene, Oregon, but the Japanese delegation has not been spared since.
It now totals 15 members who have tested positive for Covid-19, the Japanese federation announced on Tuesday.
Four new members present at the World Athletics Championships have been infected with the virus.
Among them, an official and three athletes including sprinter Yuki Koike.
At the 2019 Worlds, he won the bronze medal in the 4x100m.
Due to his infection, he was forced to forfeit the 200m, the series of which took place on the night of July 18 to 19, French time.
Three marathon runners already affected
Before the four new cases formalized on Tuesday morning, eleven cases had been announced on Monday and last weekend among the Japanese.
They concerned three marathoners, the head coach of the Japanese selection as well as other coaches and staff members.
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These fifteen patients must now observe a period of isolation of five days.
“World Athletics, the organizers and the Japanese Federation are working together to avoid other delegation members being in the same spaces as other delegations”
World Athletics and the Japanese federation said in a joint statement after the first positive tests.
Prior to the event, world hammer champion DeAnna Price also forfeited after contracting Covid.
Canadian sprinter Andre De Grasse has withdrawn from the 200m to focus on the 4x100m, diminished by his coronavirus infection less than a month ago.
