South Australia had a 99 per cent chance of enduring a "significant wave" of COVID-19 if the state had not gone into recent lockdown, according to modelling.
Chief Public Health Officer Nicola Spurrier revealed on Sunday graphs of modelling that was provided to her last week as she decided how to deal with the emerging outbreak.
The modelling drove her decision to enter a hard lockdown and "supercharge" contact tracing efforts, she said.
It showed there was a 50 per cent chance there would have been about 100 daily cases by mid-December, and a smaller but "not negligible" chance that numbers would reach 200 per day.
"What we can say is that we absolutely were looking at facing a second wave," Dr Spurrier said, claiming she had "no regrets" about her decision.
The modelling was not affected by false information provided to authorities about a pizza shop worker, who has been blamed for sending the state into lockdown, she added.
South Australians emerged from hard lockdown on Sunday.
Residents can now attend pubs and restaurants in groups of 10, hold private gatherings of up to 50 people providing there is no more than one person per four square metres, and go to beauty salons and gyms.
Schools and child care centres are set to reopen, as will most non-essential businesses which had been directed to close.
However, community sport and recreation centres are still not allowed to operate. People are being encouraged to continue working from home for the next eight to 10 days if possible.
South Australians are urged to wear masks where they cannot physically distance.
South Australia recorded just one new case on Sunday, a woman in her 20s who is quarantined in a hotel after travelling overseas.
There were no new diagnoses in the Parafield cluster in suburban Adelaide, which remained at 26 cases.
Despite the low numbers, Dr Spurrier said she would only be "fully confident" SA had escaped a second wave in a few weeks.
Police have issued around 182 warnings and 103 fines in the past two days to people "blatantly" disregarding stay-at-home directions, Premier Steven Marshall said.
There are 37 active cases, including a man in his 30s who is in hospital.
Nearly 17,000 tests were carried out on Saturday. More than 4000 contacts or close contacts of the outbreak remain in quarantine.
Investigators had spoken to a pizza shop worker on Saturday who lied to contract tracers about his whereabouts, Mr Marshall said. Police seized electronic devices from the worker.
The worker is believed to be a 36-year-old Spaniard living in Australia on a temporary graduate visa.
Police will provide a comprehensive briefing on the investigation into the pizza shop on Monday, Mr Marshall said.
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