Victoria has notched up its 33rd consecutive day without a coronavirus case, though authorities are urging vigilance after viral fragments of the virus were detected in wastewater.

The Department of Health and Human Services has revealed a wastewater treatment plant at Colac, 150 kilometres south-west of Melbourne, produced a positive sample from November 23.

Further analysis showed the sample had “very low levels” of viral fragments, DHHS said, which could point to someone in the area shedding the virus after recovering from it.

“It should serve as a reminder to all Victorians that if you have the mildest of symptoms – to get tested,” the department said.

Last week, a similar notice was issued to residents of Geelong’s northern suburbs, after traces of coronavirus were detected in Corio wastewater.

Tweet from @VicGovDHHS

The latest wastewater find comes as a woman in her 20s was put into isolation awaiting the result of a third test amid a review of her case by an expert panel.

The DHHS confirmed it was notified late on Monday of the women’s “indeterminate” result, adding her first test was a weak positive and the second a negative result.

Some 12,177 Victorians came forward for testing on Monday, as Queensland and South Australia reopened their border to the state and Western Australia confirmed it would follow suit on December 8.

Meanwhile, one of Australia’s authorities on hotel quarantine programs said training, not uniforms, would be key to the success of Victoria’s new-look system.

Jane Halton, the chair of the coalition of epidemic preparedness, has reviewed quarantine programs across the country and said the issue was not whether security guards, police or defence personnel were used as staff.

Premier Daniel Andrews outlined the state’s new program on Monday ahead of it resuming on December 7. He has billed it as the “strongest and safest” hotel quarantine scheme in Australia.

Mr Andrews is also due to confirm the winding back of more virus restrictions on December 6.

Victoria confirmed its first virus death in a month on Monday, taking the state toll to 820 and the national figure to 908.