A new case of coronavirus in Victoria has authorities spooked because the victim was diagnosed with the virus back in July.
The single new case of COVID-19 recorded on Monday was diagnosed with the virus three months ago before a second test this week proved positive.
Chief Health Officer Brett Sutton said investigations are underway to determine whether the unusual case is an 'extremely rare' re-infection or if the patient is still shedding non-infectious virus particles.
'There are those individuals who can continue to shed the virus, it is not a transmissible virus, it's a dead virus essentially,' he told reporters on Tuesday.
Chief Health Officer Brett Sutton said investigations are underway after a new case of coronavirus previously tested positive in July
'This may be a case in point, but we need to make sure, so we need to exclude the possibility that it is reinfection with a new virus for this individual.
'But if there is nothing that indicates epidemiologically that this person has been exposed to a known case, and if the fuller laboratory results really point to this just being the tail end of a really long infection, then that will come off as a false positive, but it's early days.'
The alarming case could be one of the longest shedding periods recorded in Australia, or, alternatively, the country's first confirmed double bout of COVID-19.
Out of more than 40.3 million infections globally, there have only been a small number of confirmed re-infections, with the US recording its first just last week.
'It is only a handful of cases reported around the world, so it seems to be exceptionally rare, but it does happen,' Professor Sutton said.
'We need to explore the possibility of it happening.'
The single case of coronavirus recorded on Monday could be Australia's first confirmed reinfection or a false positive from virus fragments still in the individual's system. Pictured: a drive-thru testing clinic in Shepparton
Scientists are working to understand what factors might make people vulnerable to catching the illness twice but research into COVID-19 immunity is still in its early days and experts say its longevity will only be known as time progresses.
The first confirmed reinfection was only recorded two months ago in Hong Kong, with more reinfections expected worldwide as the virus continues to spread.
While it is more common for an individual to still have the virus in their system than to be reinfected, Professor Sutton said the circumstances of the case remained abnormal.
'Not everyone who has been infected previously develops another syndrome with symptoms that are consistent with coronavirus who also gets tested,' he said.
He added that maximum duration of shedding remains unknown, but in previous cases it has extended 'several weeks'.
Premier Daniel Andrews said the state was 'well placed' to bring forward by a week the further easing of more restrictions in Melbourne after the state only recorded the one case on Monday
'For a lot of places in the world the peak of their pandemic has been just in recent weeks and so that time of seeing how long someone might continue to shed the virus isn't particularly well understood,' he said.
'But it known to be several weeks for some individuals.'
Aside from the concerning infection, one other COVID-19 case was reported by the DHHS on Monday involving a Victorian who is quarantining interstate, having recently returned from overseas.
Premier Daniel Andrews said the state was 'well placed' to bring forward by a week the further easing of more restrictions in Melbourne slated for November 2, after several restrictions were either reduced or ended on Monday.
'I would just say when you look at these numbers, this could potentially be a day of zero and it's been a long time since we had a day of zero,' Mr Andrews said.
'It's a testament to the hard work of every single Victorian in the city, in the suburbs, in regional communities, large and small.'
Men queue for a haircut outside a barber shop in Melbourne on Monday as some of the city's three-month old stay at home restrictions were eased due to falling COVID-19 infection rates
However, Mr Andrews ruled out the possibility of hospitality reopening in time for the AFL grand final on Saturday.
'It's important we see this thing off properly. Sunday can be a day where we'll have more to say,' he said.
'No one game of footy, no one barbecue or dinner with friends is worth all that can be on offer in a COVID-safe summer and a COVID-safe and COVID-normal 2021.'
There are 122 active cases in Victoria, a drop of 14 from Monday.
Melbourne's 14-day rolling average of new cases also dropped below seven to 6.4 and the number of mystery cases in the city from October 4-17 also fell by two to 13.
No deaths were recorded on Tuesday, with the state's death toll remaining at 817, while the national figure is 905.
Eleven Victorians are in hospital fighting the virus, though none are in intensive care.