Just hours before the toss at the Adelaide Oval on Thursday, officials were trying to determine whether Cummins would be required to isolate after going to dinner on Wednesday night.
It's believed the quick was at an Adelaide restaurant when a person at the next table was identified as a positive coronavirus case.
Those around the case were quickly notified, and Cummins immediately left the venue and alerted officials.
Under South Australian Health protocols, close contacts must isolate and quarantine for seven days after their interaction with a confirmed case.
Health officials will determine if Cummins is a close contact depending on the amount of time he was exposed to the infected person, how close he was, if masks were worn and generally study the restaurant setting.
CA was unable to comment when contacted on Thursday but was looking into the matter and whether Cummins could take his place against England.
If Cummins is ruled out of the Test, Steve Smith will captain Australia for the first time since the Cape Town ball-tampering scandal in 2018.
Michael Neser - who lost out to Jhye Richardson to replace Josh Hazlewood - is be expected to earn his Test debut if Cummins is unavailable.
Cummins' absence along with that of Hazlewood would be a massive blow to Australia after the world's top-ranked Test bowler claimed a five-wicket haul in the series-opening win at the Gabba.
He has also taken 46 wickets at an average of 16.23 in day-night Tests, and was expected to reclaim the new ball for the pink-ball match.
Adelaide has had a rise in COVID-19 cases over the past week, with the 25 reported on Wednesday the most in a single day in more than 18 months.
Players are not in strict bubbles for the Adelaide Test, with both Australian and England players wanting as many freedoms as possible on the tour.
But the Cummins incident does call into question what protocols will be required for the next two Tests in Melbourne and Sydney, where cases are beyond 1000 per day.
Officials would also be keen to avoid a repeat of the cancelled Test between England and India this year, after fears of an outbreak in the India camp.
Coach Ravis Shastri has since denied claims it was spread at the launch of his book in London.
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