In an urgent plea late Saturday, chief public health officer, Professor Nicola Spurrier, said testing was vital for even a mild illness.
Her warning emerged as a new twilight Christmas Pageant is set for approval.
Virus sleuths have combed wastewater since April at stations across SA to help identify traces of the disease’s genetic material and identity new cases earlier.
But for the first time since the height of the pandemic’s first wave in March, two positive waste samples have been discovered in the past 10 days in Adelaide and the Barossa Valley, SA Health revealed Saturday.
Authorities tonight launched an urgent testing operation to rule out community transmission, in which an infection source is a mystery.
Mobile test clinics are set to be launched in the Barossa – the source of one of SA Health’s five clusters – while existing facilities will have resources boosted.
The first case, found on August 26, came at the Bolivar plant, which is a catchment for 700,000 homes and businesses across the northern and eastern suburbs and CBD.
The “weak positive” result was restested and returned a negative reading on Tuesday.
The second case, at an Angaston plant – which treats wastewater from 2000 homes – was discovered on Thursday before another test returned a positive result on Saturday morning.
Dr Chris Lease, who will be acting in Prof Spurrier’s role for the next week while she is on leave, said while the results might have a “variety of sources”, authorities could not rule out community transmission.
A source might be a knowncase in hotel quarantine, a visitor or a transport worker.
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“It is a very difficult thing to determine where the sources might be,” he said.
As test levels nearly hit 400,000, Prof Spurrier – who said her advice on easing virus restrictions or border bans was unchanged – said high rates of testing could only rule out any unknown outbreaks.
“If we start to get more positives then that will be a serious indicator that we have got community transmission,” she said.
“But at the moment, it is too early to tell.”
The infectious woman, in her 20s, became the state’s 464th case after 12 days of zero new patients and three days of SA being virus-free.
She illegally flew from Melbourne on Thursday on a Jetstar flight JQ774 bound for the Northern Territory with four young cousins, aged between 10 and 17.
Due to fly from Adelaide Airport to Alice Springs, where other family live, none had travel permits. Rules ban travellers from Victoria without special SA Health medical or compassionate exemptions.
The family, none of whom have been fined for border breaches, were last night in quarantine at the Pullman Hotel, Hindmarsh Square.
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