NSW COVID-19 transmission: The search for patient zero

New South Wales health authorities are desperate to find patient zero and link them to the state's first new case of community-transmitted coronavirus in five weeks.

A man in his 50s from south-east Sydney had been "very active in the community" before testing positive on Wednesday, Premier Gladys Berejiklian said.

Health authorities believe he's been infectious since last Friday but the biggest fear is they have no idea how he contracted COVID-19 or where from.

READ MORE: More venues in Sydney visited by man with coronavirus

"He hasn't returned from overseas, he hasn't worked in border or quarantine roles, he has not had any contact with the hospital system," Chief Health Officer Dr Kerry Chant said.

The number of venues he visited while infectious continues to grow, almost doubling on Wednesday night to more than a dozen throughout the weekend.

NSW Health also revealed fragments of the coronavirus had been detected in the Marrickville sewage network, servicing about 42,000 people.

People in Dulwich Hill, Marrickville, Summer Hill, Lewisham, Ashfield, Haberfield, Petersham, Lilyfield and Leichhardt are to be "especially vigilant" in monitoring for symptoms.

READ MORE: States and territories react to new Sydney coronavirus case

Anyone who attended one of the following venues at the times specified is asked to immediately get tested and isolate until NSW Health provides further information.

Friday, April 30:

- District Brasserie, Chifley Square, 11am – 11:45am

- HineSight Optometrist, Sofitel Sydney, Wentworth, 12pm – 1pm

- Barbetta, Paddington, 1:30pm – 2:30pm

- Screening of The Courier at Event Cinemas, Westfield Bondi Junction, 6pm – 8pm

- Figo Restaurant, Rushcutters Bay, 8.45pm – 11pm

Saturday, May 1:

- Joe's Barbeques & Heating, Silverwater, 1pm – 1.45pm

- Tucker Barbecues, Silverwater, 1pm – 1.45pm

- Barbeques Galore, Annandale, 2pm – 3pm

- Barbeques Galore, Casula, 4pm – 5pm

- BP Mascot, Botany Road, 4.30pm – 5pm

Sunday, May 2

- The Meat Store, Bondi Junction, 3pm – 4pm

Monday, May 3

- The Stadium Club, Moore Park, 11.30am-12.30pm

- Azure Café, Moore Parl, 12.30pm-1pm

- The Royal Sydney Golf Club, Rose Bay, 5.30pm-9pm

Tuesday, May 4

- Rug Cleaning Repairs Hand Rug Wash Sydney, Brookvale, 12.30pm-1pm

- Alfresco Emporium, Collaroy, 1pm-1.30pm

- SMITH MADE, Balgowlah, 2.30pm-2.45pm

- Chemist Warehouse, Double Bay, 3.45pm-4pm

- Woolworths, Double Bay, 4.05pm-4.15pm

Even if you've been vaccinated, get tested

The man used QR codes to check in and out of venues, making contact tracing easier, Ms Berejiklian said.

"This person did everything right, but it goes to show we can't take anything for granted."

Contact tracing is underway at a number of locations across Sydney.

Health Minister Brad Hazzard said it was "a very clear reminder" that the risk of coronavirus remains, and people should get tested regardless of whether they have been vaccinated or not.

"People in the eastern suburbs particularly should be listening to these messages and getting tested," Mr Hazzard said.

READ MORE: Beer and donuts offered as incentive to get COVID jab

READ MORE: Over 50s now able to get coronavirus jab

Dr Chant said the man had a "reasonable" number of close contacts as well as venue contacts that were still being investigated.

Federal Health Minister Greg Hunt expressed his confidence in the NSW coronavirus response system after the mystery case was diagnosed in Sydney.

"Contact tracing is already underway," Mr Hunt said.

"We know the strength of the New South Wales system, the absolute global gold standard."