The worker at Anglicare's Newmarch House aged care facility in Caddens was originally said to have gone to work for six days with symptoms of illness, before she tested positive for the coronavirus.

NSW Health said the woman worked with very mild symptoms while infectious but police in the latest update on Wednesday said they understood she was not symptomatic at work.

She was tested after her most recent shift, when she learned of contact with a person unrelated to the facility who had been confirmed to have COVID-19, NSW Police said.

Five additional staff members and four residents at the facility have also tested positive.

NSW Chief Health Officer Dr Kerry Chant said the woman was "absolutely mortified".

"I would urge people to remember that the symptoms of COVID-19 can be incredibly mild and the key point is 'do not go to work'," Dr Chant told reporters on Wednesday.

"I would particularly urge (that) if you work associated with providing care to the elderly, the aged and disability ... to have that incredibly high awareness of even minor changes in your health."

The health worker is "incredibly distraught" about the circumstances, Dr Chant said.

While Dr Chant said the woman "worked whilst she had very mild symptoms", Anglicare Sydney chief executive Grant Millard on Wednesday said she did not display any symptoms during her last shift at the facility.

"Nothing was disclosed to us when she was last seen on April 6th, she did not display any symptoms," Mr Millard told ABC TV.

The woman was seen by a residential manager at the time, he said.

"They displayed no symptoms, at that time they requested some time off work. We're not sure why they did that," Mr Millard said.

Anglicare on Sunday traced all workers in Newmarch House, including anyone who'd had contact with those infected at the home.

Some 40 staff at the facility have been stood down to self-isolate at home, Mr Millard said.

Approximately 100 residents - who have an average age of 85 - are isolating in their own rooms.

They are being tended to by staff wearing protective equipment.

"We brought in extra physios, extra staff in order to deal with this very challenging situation - it's very, very tough," Mr Millard said.

"People are rightfully upset. We're very concerned, but the critical issue at this stage is to ensure that we have the testing results for everyone in the home who has been tested yesterday."

Some family members of those in the aged care home are "very distressed by this", Mr Millard said.

NSW Police Commissioner Mick Fuller on Wednesday said officers would visit the home for the sake of transparency.

Police later said they had spoken with Anglicare's chief executive and the facility manager, and had received information on possible contacts with residents and other staff, and workplace health and safety arrangements.

"No further police action is expected to be required," a NSW Police statement said.

The woman also worked two shifts at Greystanes Disability Services in Leura.

Australian Associated Press