The latest wastewater testing in central Adelaide has shown no signs of the coronavirus after strong positive results were recorded earlier this week.
SA Health says testing overnight on Thursday found no traces of the virus but monitoring will continue.
The previous positive results prompted concerns with calls for anyone who had visited the city over the past week to get tested for COVID-19 if they showed even the mildest of symptoms.
The most likely explanation for the earlier positive tests was virus shedding from old infections.
That could have come from people who had travelled into the city for the Adelaide Festival and Festive Fringe activities, including some from interstate.
Two new COVID-19 cases were reported on Friday, both in men who recently returned from overseas and who remain in hotel quarantine.
One was considered an old infection with serology tests underway to determine if the second case was also old.
South Australia administered 860 vaccine doses on Thursday, a jump from previous daily figures.
It took the total so far to 5822, about half the 12,000 the government had hoped to administer in the first three weeks of the program.