Centre Irae Simone and reserve back Bayley Kuenzle return for Saturday's match in Hamilton after reportedly being among a small group of players who contracted the mumps and were ruled out of last weekend's loss to the Highlanders in Canberra with what was then a mystery illness.

However, lock Darcy Swain, who was a late scratching last week with the illness, didn't cross the Tasman on Thursday.

Winger Tom Wright started against the Highlanders in Canberra but has stayed at home, reportedly because of the outbreak.

The diagnosis of a mumps outbreak was made public by Rugby Australia on Wednesday, the diagnosis having taken that long as blood test results were needed as confirmation.

The policy of Super Rugby teams in Australia and New Zealand is to ensure all players are vaccinated against mumps but the immunisation isn't foolproof.

The ill players and coaching staff had been placed in isolation soon after they became unwell.

McKellar didn't want to identify who was affected but believed the situation was in hand.

"Well and truly, the boys exhibiting any symptoms have been left at home," the coach told AAP soon after the Brumbies arrived in Hamilton.

"We've checked every box and quarantined guys that needed it. Anyone who's in New Zealand has been blood tested.

"Roughly three or four (have stayed at home), there are names that have been mentioned previously that are unable to tour but we're hoping we're at the back end of it."

Three changes to McKellar's starting team include Simone's return in place of Len Ikitau and Andy Muirhead's promotion to the left wing ahead of Wright.

In a non-mumps related change, the in-form Folau Fainga'a has been ruled out with a toe injury.

Wallabies hooker Fainga'a, who scored a hat-trick of tries from lineout drives last week, is replaced by Connal McInerney.

With the Brumbies sitting out a bye next week, McKellar expected Fainga'a would be fit for their subsequent match against the Sunwolves.

It will be a relief to Rugby Australia and SANZAAR if the mumps outbreak has been quelled.

After consultation with ACT Health, they sought confirmation from every Brumbies player and staff member that they had been immunised or contracted the mumps previously.

The Brumbies' three opponents this season - the Reds, Rebels and Highlanders - have not reported any cases of the mumps.

A Highlanders spokesman told AAP all of their players had nevertheless taken precautions after learning of the outbreak.

Chiefs coach Warren Gatland said medical staff had assured their players that all of them had been immunised.

BRUMBIES: Tom Banks, Solomone Kata, Tevita Kuridrani, Irae Simone, Andy Muirhead, Noah Lolesio, Joe Powell, Pete Samu, Will Miller, Rob Valetini, Cadeyrn Neville, Murray Douglas, Allan Alaalatoa (capt), Connal McInerney, James Slipper. Res: Lachlan Lonergan, Scott Sio, Tom Ross, Nick Frost, Lachlan McCaffrey, Ryan Lonergan, Bayley Kuenzle, Toni Pulu.

Australian Associated Press