Queensland could be headed for another lockdown if a flight attendant passed the highly contagious Delta variant to passengers on six flights across the state.
Authorities are scrambling to determine if the QantasLink worker has spread COVID-19 to the regional centres of Gladstone, Longreach and Hervey Bay.
The woman also spent time in the Brisbane suburb of Banyo, where she lives.
Chief Health Officer Jeannette Young says the attendant didn't seek a test until Wednesday - nine days after she began showing symptoms on July 13.
It's believed the woman would have been infectious two days before that, putting at risk every passenger and colleague on six flights she crewed on July 11 and 12.
The worker has told health investigators she was "essentially" at home in Brisbane from July 13 onwards.
"We're just working that through to see that that is the case," Dr Young said while ordering Brisbane residents to closely monitor the list of exposure sites in case the woman did leave home.
Dr Young did not yet know why the woman waited so long after the onset of symptoms to get tested.
Health teams are going through the passenger lists for the at-risk flights.
Dr Young said it was essential that every one of those people underwent testing.
Among those who already have is Queensland's Regional Development Minister Glenn Butcher, who was on one of the flights between Brisbane and Gladstone. He's waiting for his results.
Genomic sequencing has confirmed the flight attendant has a form of the virus identical to 60 cases from the NSW cluster, and she travelled to NSW in the course of her work.
But the exact route of transmission is not clear and there's one aspect about the case that has confused Dr Young - the lack of other cases given how much time has passed.
"We know that with the Delta variant it usually spreads within two days. In Victoria they're seeing spread from one person to the next in 30 hours," she said.
"I would have expected there'd be spread and then spread and then spread, and I've not seen that. If not one single person on any of those six flights tests positive today, that would be very reassuring."
Dr Young told Queenslanders it was too soon to order another lockdown, but if more cases emerged "we'll do it fast if we need to do it. I just need a bit more information."
QantasLink said the infected flight attendant flew on six regional services on a 74-seat Dash-8 Q400 aircraft.
"There have been no other reports of positive COVID cases from these flights ... the cabin crew member did not leave the airport in Longreach or Hervey Bay," it said.
Other crew are being tested and must isolate for 14 days from the last shift they worked with the woman, which in this case is three or four more days.
"Qantas has previously called for priority access for crew to receive COVID vaccination, given their role of flying to multiple cities and towns in a day," the airline said.
Meanwhile, fragments of the virus have been found in sewage in the Byron Bay area.
Acting Premier Steven Miles said the situation was being monitored closely and it was vital that residents in northern NSW and southern Queensland only used the cross-border travel bubble for essential trips.
Additional testing capacity is being stood up in Gladstone, Longreach and Hervey Bay.
The flight of concern on Sunday 11 July are QF2534, from Brisbane to Longreach, QF2535 from Longreach to Brisbane, and QF2346 from Brisbane to Gladstone.
Flights of concern on Monday July 12 are QF2331 from Gladstone to Brisbane, QF2374 from Brisbane to Hervey Bay, and QF2375 from Hervey Bay to Brisbane.
Queensland's borders remain closed to NSW, Victoria and South Australia.
