The figures, confirmed by the Department of Health and Human Services on Wednesday, brings Melbourne's 14-day case average to 9.9, a drop from 10.6 on Tuesday.Melbourne's number of mystery cases between September 21 and October 4 sits at 12.

The city needs a 14-day average of five cases and no more than five mystery cases during the same period to further ease restrictions on October 19.But a growing outbreak linked to a Melbourne butcher shop continues to trouble authorities.

Chief Health Officer Brett Sutton on Tuesday confirmed 28 cases were linked to the Butcher Club at Chadstone Shopping Centre, up from 24 on Monday.It consists of at least eight staff, 11 close contacts and four customers.

The outbreak has leaked into regional Victoria, with two people in Kilmore - 60km north of the city - testing positive after an infected Melbourne person illegally dined at a local cafe.

Burnet Institute epidemiologist Mike Toole labelled it a "modest super spreading event", but noted NSW had successfully bought bigger outbreaks under control.

"Not so long ago, more than 60 people were infected with a cluster at the Crossroads Hotel in Sydney (and) more than 100 infected from a cluster linked to a Thai restaurant," he told ABC radio on Tuesday.

"So, so far 28 is not in the big league."Professor Toole said health authorities are "very lucky" the butcher shop wasn't in an enclosed environment.

"If it had been a closed-in butcher shop in a small retail strip somewhere else in Melbourne it could have been much worse," he said.

Nonetheless, Prof Toole said the outbreak was still "concerning" and suggested contact tracing had to be "perfect" to find every infected individual.

"What I would hope is that all community resources are mobilised and recruited in this effort," he said."What I mean by that is community-based organisations, people that speak the right language, ethnic leaders, church leaders ... they all have to be mobilised.

"Professor Sutton said he "really can't say" if the city will now meet its "step three" case targets by October 19 as initially planned.

Prof Toole believes Victoria remains on a "good trajectory", but admitted authorities "could have a problem" if each Chadstone case infects one or two others.Meanwhile, about 85,000 VCE students will return to school on Wednesday for the General Achievement Test.

Everyone who feels even the slightest cold or flu-like symptom must assume they have the virus until a test result proves otherwise. Anybody with symptoms or awaiting a result should self-isolate at home.

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