A worker at Doutta Galla Aged Care in Footscray is among Victoria's new coronavirus cases and has been identified as a close contact of one of the Cedar Meats workers who have tested positive.

Doutta Galla Aged Services said in a statement the staff member has no symptoms and remains isolated at home.

"The staff member last worked at the home on April 26 and has not worked since that date," the statement says.

"There is not an outbreak nor a COVID-19 cluster, and no resident or staff are showing signs of infection."

Health Minister Jenny Mikakos on Wednesday said residents and staff at Doutta Galla are being tested, and claimed the government had managed the meatworks outbreak "perfectly".

The positive at Doutta Galla has put the facility in lockdown until May 11.

Another aged care centre northwest of Melbourne also is in quarantine.

A worker at Grant Lodge aged care in Bacchus Marsh was tested for COVID-19 on Saturday and it has come back positive.

The worker was tested as part of a Victoria's ongoing screening program, despite being asymptomatic, Djerriwarrh Health Services confirmed.

"All Grant Lodge staff members who have interacted with the infected staff member are being tested, and sent home for isolation, and the Lodge is in lockdown," they said in a statement.

Victoria recorded 17 new COVID-19 cases on Wednesday, including four cases from Cedar Meats in Melbourne's west.

Of the 49 cases linked to the outbreak at the facility, 45 are workers and four are close contacts.

But Victorian Chief Health Officer Professor Brett Sutton hosed down concerns the outbreak stemmed from a worker who tested positive for the virus on April 2.

The person who tested positive on April 2 said they hadn't been at work while infectious, so the workplace was not considered an exposure site.

The second case linked to the workplace was diagnosed on April 24, followed by a third case about 24 hours later.

That person had been a patient at Sunshine Hospital for unrelated reasons prior to diagnosis or displaying symptoms.

It wasn't until April 29 that the department took additional actions, including testing all 350 Cedar Meats staff.

Prof Sutton said it's not clear exactly how the outbreak emerged,

"We have no idea," he said.

"He might be connected through some unknown linkage outside of work, or who knows."

Cedar Meats is now shut and Prof Sutton expects that will bring the outbreak to a head, after some more cases emerge in the next fortnight.

Opposition Leader Michael O'Brien said the cluster was "(Premier) Daniel Andrews' own Ruby Princess", referring to the cruise ship that docked in Sydney and is now the subject of a special commission.

Minister Mikakos dismissed the comparison, saying "the public health team has done an excellent job in responding to this outbreak."

The Ruby Princess virus cluster is linked to more than 20 deaths and 600 infections across Australia.

Of the 1440 coronavirus cases in Victoria, 145 may have been acquired through community transmission.

The low number of community transmissions is seen as a good sign by Prof Sutton, who hopes for some easing of restrictions after May 11.

Meanwhile, Federal Agriculture Minister David Littleproud is investigating whether commonwealth officials inspecting abattoirs might have been affected.

"I'm just getting to the bottom of when we were notified because obviously they make an inspection at one abattoir and move to another," he told reporters in Canberra.

"Those commonwealth and department of agriculture personnel who were in that abattoir and then moved to another one potentially could have spread the virus. So I want to get an understanding of what Victorian state officials undertook in that."

Australian Associated Press