A man who recently returned to Australia from Pakistan has tested positive to COVID-19 after arriving in Adelaide.
SA Health says the man, 35, first arrived in Melbourne on June 6 and tested positive there on June 9.
But because he first developed symptoms in May, he was allowed to serve a shorter period in quarantine before moving on to Adelaide and flew into SA on Tuesday morning.
He was tested again on arrival at Adelaide Airport, returning a positive result.
However, Chief Public Health Officer Nicola Spurrier says he is no longer infectious and is not being considered a new SA case.
She says local health authorities are confident he poses no risk to other people but he will spend two weeks in isolation at home as a precaution.
No other people, including those on the same plane, are being required to isolate.
Prof Spurrier said the man was considered to have cleared the disease before he left Melbourne and she was happy with how Victoria had handled his case.
"We do have people that test positive for COVID-19 for a very prolonged period of time. It can be seven or eight weeks," she said.
"This person was not considered infectious when they travelled (to SA).
"When you have a nasal or throat swab it picks up the virus particles but we know from research that it's only for about eight days that the virus is at all viable.
"After that time it's basically dead parts of the virus."
Prof Spurrier said with the new case not added to SA's tally, the state's total remained at 440 and there were no active cases.
This case aside, South Australia has not reported a new virus infection for more than three weeks.
Details of the man's case came after SA on Wednesday opened its borders to travellers from Western Australia, Tasmania and the Northern Territory.
People who come to SA from those regions are no longer be required to spend 14 days in quarantine.
Other borders are due to open on July 20, though Premier Steven Marshall has flagged an earlier date for Queenslanders.
"We will lift our borders when it is safe to do so and we've done that with Western Australia, Northern Territory and Tasmania," the premier said.
"I don't think it will be long until we remove the border with Queensland."