Covid 19 coronavirus: Mystery at centre of NSW cluster as authorities hunt for patient zero

A sign displayed at Palm Beach in Sydney, Australia following an outbreak of Covid-19 cases on the northern beaches which has grown to 28 people. Photo / Getty

Health authorities are still searching for patient zero in the NSW virus cluster that has prompted states to enforce new quarantine requirements as cases are expected to rise over the weekend.

Genomic sequencing points to viral spread at an event at the Avalon RSL on December 11. Eight attendees later tested positive for the virus. Two people from that group then visited the Avalon Bowling Club two days later, and are part of a group of 16 who also tested positive for Covid-19.

Infectious people then fanned out across the city, visiting cafes, restaurants and public toilets in Cronulla, Woolloomooloo, Turramurra, Darling Point, Eveleigh, Rosebery, Bondi Junction and Riverstone.

NSW Premier Gladys Berejiklian warned yesterday if the state didn't get a hold of the cases in the coming days, it could mean more restrictions.

"If we get on top of this in the next two or three days, all of us will be able to have a much better Christmas, but if we don't get on top of it in the next few days, it could mean further restrictions down the track."

NSW has urged all residents to monitor for symptoms and come forward for testing as a new list of affected venues has been published in NSW and Queensland.

Northern beaches residents have been asked to stay home as much as possible over the weekend, as the list of potential sites stretches from Sydney's northern beaches to Bondi Junction, Cronulla and Queensland.

NSW Health Minister Brad Hazzard announced 14 of the 17 pubs in the northern beaches had closed voluntarily for the weekend on Friday. He said most churches and houses of worship had also made the decision to shut their doors.

Anyone who knows what Manly Corso would normally be like on the last Friday before Christmas knows how impressive this is.

Remember there is no lockdown. This is voluntary.
Manly is over 20km from Avalon.
Most people are doing the right thing. pic.twitter.com/bnFtLgXHaC

— Carrick Ryan (@realCarrickRyan) December 18, 2020

NSW chief health officer Kerry Chant said "my anxiety is that we haven't found the direct transmission route".

Without that information, it's difficult for contact tracers to know they have "locked every transmission line".

People line up at a Covid-19 testing site at Mona Vale Hospital on December 18 in Sydney. The number of positive Covid cases is expected to rise over the weekend. Photo / Getty

University of Queensland virologist Professor Ian Mackay told the ABC finding the original source was critical.

"If we can find the index case, that means we can work forward from there to make sure all the contacts have been identified," he said.

"If we can't find the source, there's always a possibility that some cases have been missed."

It's also important to know to ensure there are no holes in the system that could see cases slip through from overseas undetected.

Cars line up on approach to a Covid-19 pop-up testing location at Pittwater Park in Sydney as testing ramps up. Photo / Getty

"Where did this case come from? Is it through a leaky quarantine system? We assume it is because we don't seem to have cases ticking along in Australia. But perhaps we do," he said.