University of Sydney virologist Rebecca Rockett, who is involved in COVID-19 genomics testing, said all cases in Victoria had very similar genetic signature which accurately determined it came from a point source infection.

“That’s good news in terms of the fact they’re not dealing on multiple different fronts with different importations of the virus which happened in the first wave,” she said.

“From the limited data we have at the moment, they look like they’re the same strain (in Victoria and NSW)...which is a good thing in our eyes.

“We don’t want to see different strains coming in where we don’t understand where the transmission chains have come from.”

Deakin University’s Epidemiology chair Professor Catherine Bennett said while it was not 100 per cent proven that all Victorian cases were linked to the same virus, there have not yet been any other genomic sequences — or fingerprints — found in the community.

“In a process by exclusion we’re saying this is caused by a single breach,” Prof Bennett said.

“The COVID virus doesn’t mutate as quickly as others might… but it’s stable enough for the virus that came into Melbourne in late May to still be identifiable in NSW cases.”

Genomic testing in relation to COVID-19 looks at the genetic code of the virus and the small changes within genome that occur.

Dr Rockett said it was being used to help determine how the virus moves through the community.

She said it was traditionally used to source foodborne outbreaks, such as salmonella.

“The epidemiology will do an analysis and then do some environmental swabbing. We’ll match the genome from the patients with particular salmonella species that could be cultured from fresh fruit, vegetables or chicken,” Dr Rockett said.

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“Then when we find that match, we can accurately source where the outbreak is.

“We used that premise when COVID-19 struck in Australia to quickly design this test that will help us group together clusters of patients were we think they transmitted the virus to each other which adds extra evidence to traditionally epidemiology.”

Professor Bennett said genomics helped assess if cases were linked.

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“It tells you that you have a point source, that there has been a breach on quarantine,” Prof Bennett said.

“It can link information about the strain of the virus back to libraries that are being built with the bio-information in them which tells us what strains of viruses are circulating in other parts of the world.

“As the outbreak goes on, it’s harder to determine which country of origin this particular strain came from because you’re looking for fingerprints but you can only match them with the fingerprints that have been uploaded (in the libraries).”