A returned traveller from the US is the suspected patient zero of Australia's Sydney cluster – but how the coronavirus might have spread from her to the Northern Beaches community is still a mystery.
NSW virus experts have cast a wide net around the woman, who landed in Sydney from LA on December 1.
Numerous people who have had contact with her, from drivers and hotel cleaners to health workers, have been interviewed and tested, NSW chief health officer Kerry Chant said.
"We've gone back and reviewed all the CCTV footage around this individual," Dr Chant said.
"We've tested cleaners at the hotel. We've tested people who transported her when the person went to a health facility. We've looked at anyone who may have come in contact with her – even if they were wearing PPE."
The woman's fellow passengers all went into quarantine as required, Chant said. The airline had assured her the flight crew had abided by self-isolation rules.
Chant was careful to underline that it's not certain the woman is actually patient zero.
But the virus strain she had been infected with is a close match to the virus that is causing havoc in the Northern Beaches area.
"[The genomic testing] is not a perfect match with that returned traveller. But it's close," Chant said.
The key question that remains unanswered is how the virus spread into the community.
NSW Health Minister Brad Hazzard said earlier in the day that one theory is it could have been spread via touch.
"It could be anything. We just don't know," Hazzard told 2GB radio on Monday morning.
"Did someone pick up a bag she put down? Perhaps at the airport, where someone might have crossed over?"
Hazzard has previously described what tracers are searching for as a "missing link" in the virus transmission.
Chant has said finding that link might be a "challenge beyond us".
Asked about a Daily Telegraph report that thousands of international flight crew members and hundreds of diplomats have been able to skip hotel quarantine and instead isolate at home, Hazzard said there was nothing indicating that might be connected to the new outbreak.
"We don't believe so, we've got no evidence of that," he said.
Elaborating on that issue in an interview with Channel 9's Today show, Hazzard said diplomats had regular check-ups to make sure they stayed in quarantine and got tested for Covid-19.
He also said diplomatic issues were primarily the responsibility of the Federal Government.
"It hasn't been a huge problem for us at this stage. Having said that, we are always potentially looking at the possible loopholes, but we also have to understand that we live in a diplomatic world where the diplomats at a federal level have slightly different requirements," Hazzard said.