It is not certain the infected Victorian man caught coronavirus in hotel quarantine in Adelaide, but once in Melbourne he took two trains and visited an Indian restaurant.
However, Health Minister Martin Foley said he expects the hotel quarantine to be the source of infection, but he is not taking it as a given.
“We want to chase every rabbit down every burrow and make sure we leave nothing to chance,” he said.
“The last thing we want is to put all of eggs in the genomic sequencing basket.”
One of the other potential sources of infection is a flight the man took from Adelaide to Melbourne, though it is not considered likely.
Mr Foley also suggested the man had a “very, very long incubation period”, and had contracted coronavirus overseas but not tested positive during quarantine.
Meanwhile, no new cases have been detected in NSW overnight.