The Mitchelton-Scott team and title contender Steven Kruijswijk have withdrawn from the Giro d'Italia after the latest round of Covid-19 testing.
Jumbo-Visma's Dutchman Kruijswijk and Team Sunweb's Michael Matthews tested positive as did four staff members of the Australian team, from 571 tests.
"As a social responsibility we've made the decision to withdraw," said Mitchelton-Scott boss Brent Copeland.
Their British rider Simon Yates tested positive before stage eight.
Kruijswijk, ruled out of last month's Tour de France because of a shoulder injury, said: "Within the team we take a lot of measures to avoid contamination.
"And I just feel fit. I can't believe I got it. It is a very big disappointment to get this news. It is a pity that I have to leave the Giro this way."
In a statement on their website, Team Sunweb said: "Michael is currently asymptomatic, feels healthy and is now in quarantine."
A staff member from Team AG2R-La Mondiale and Team Ineos Grenadiers also tested positive and are now isolating.
The latest rounds of tests were carried out on 11 and 12 October.
Portugal's Joao Almeida of the Deceuninck-Quick-Step team currently leads the general classification by 30 seconds after nine stages.
The Grand Tour race, originally scheduled for May, finishes on 25 October.