NSW has recorded no new cases of COVID-19 for the first time in three months as health officials urge people to remain vigilant as the school holidays start.
The welcome result was for the 24 hours to 8pm on Saturday from 12,333 tests, NSW Health said in a statement on Sunday.
It puts the number of confirmed cases in NSW at 4029 and the death toll at 55 for the state, with 68 cases still being treated, including three in intensive care but none on ventilators.
NSW Health's Dr Christine Selvey thanked the community for their efforts in reducing COVID-19 numbers but asked people to remain vigilant and come forward for testing if they had a runny nose, scratchy throat, cough or fever.
"This is particularly important for the start of the school holidays and increased movement of people around the state," she said.
Meanwhile, traces of COVID-19 have been detected in raw sewage across Sydney, as well as Shellharbour, as part of new research that could provide another tool in the fight against the pandemic, NSW Chief Health Officer Kerry Chant said.
She said the sewage testing program undertaken by NSW Health and Sydney Water started in July could show where the virus had been and provide early warning in places without known or recent cases.
"This is early days for this research, and we have a lot of work to do analysing our findings, but it's one more way we can strengthen our fight against COVID-19," Dr Chant said in a statement.
"This is a program that will show us where COVID-19 has been. For instance, we would expect to see viral fragments in Sydney sewage where we have consistently had cases in the community or in hotel quarantine
"However, if we continue to have very few active cases, there is scope for this testing to provide early warning in places without known or recent cases."
Sydney Water's General Manager Customer, Strategy and Engagement, Maryanne Graham, said treatment processes effectively deactivated the virus and there was no risk to testing staff.
She said Sydney Water was also supporting NSW Health by analysing samples from regional areas including the Hunter, the North Coast, Southern and Western NSW.
A mystery infection on Friday ended a three-day run for NSW without community transmission.
The man in his 50s had not had contact with a previously confirmed case.
There are concerns his infection could reset NSW's "border clock" with Queensland if authorities can't determine how he got sick.
Queensland chief health officer Jeannette Young says she will await the result of an investigation.
NSW must record 28 days with no community transmissions before its border with Queensland is reopened - a feat Premier Gladys Berejiklian says is a "pretty tall order".
Australian Associated Press