Contact tracers are following dozens of lines of inquiry and officials are poring over CCTV footage as the NSW government scrambles to find the source of the growing cluster in Sydney's Northern Beaches.
Such is the mystery surrounding the outbreak that the state's chief health officer has speculated that finding 'Patient Zero' could be a "challenge beyond us".
Premier Gladys Berejiklian announced another 30 cases of community transmission on the peninsula on Sunday, bringing the number of cases associated with the cluster to 68.
Almost all of the new infections – 28 – are directly linked to the Avalon cluster while two are under investigation, but were diagnosed in people living near Avalon.
Genomic sequencing suggests the strain circulating in the community is of US origin might have come into the country via an infectious returned traveller who landed in Sydney on December 1.
However, chief health officer Kerry Chant said there was still "no-one" pinpointed who could have brought that virus strain to the Northern Beaches.
"There is no-one else we have identified that could be the source," Dr Chant said.
"At the moment we are forensically looking at all of the journeys of that individual to see if there were any points associated with it.
"There is an intensive investigation underway and while a really do want to find the source, it may be that this is going to be a challenge beyond us."

People line up at a Covid-19 testing site at Mona Vale Hospital on December 18 in Sydney. Photo / Getty Images
Dr Chant said the returned traveller, a woman, was infectious on the plane and stayed in hotel quarantine upon her arrival.
"We are trying to look and crossmatch any list, look for any people that may have been associated with anything to do with airports or quarantine facilities," she said.
"The investigation is far-ranging and we have a dedicated team and assistance looking at CCTV footage.
"We are being as thorough as we can. We probably have … at any one time, 10 or 20 lines of inquiry and we pursue them all concurrently.
"There is no one who wants to get to the bottom of this more than myself because if I understand the clear chains of transmission I can then better inform government about the risk.
"The problem we have at the moment is that I do not know how we got there so I do not know the person nor where that person has been."
Health Minister Brad Hazzard was asked whether the virus could have made its way to the Northern Beaches via a person who was exempted from hotel quarantine.
He told reporters there was "not a single case" where an exempted person had brought a positive case into the community.
Berejiklian was more confident about the prospects of finding the source.
"Of course it is a concern to us that health experts are yet to identify how the cluster was transmitted into the community or how it started in Avalon (but) we certainly will get to the bottom of that," she said.
Acting chief medical officer Paul Kelly said it was most important to find out where the cases had been while infectious.
"And also as is the normal case now, particularly in NSW, looking back from when they became infected to where they had been in the week or two before that," Professor Kelly said.
"That will give us many clues and hopefully that will also include where this missing link, if you like, may be."

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