Victorian health authorities remain alarmed at two worrying trends in the state’s latest COVID outbreak.

Of particular concern are the mystery cases that are being found each day – along with many of the most recent infections in permitted workers in healthcare, construction and other essential industries.

Health official Kate Matson pleaded with Victorians to present for testing as soon as virus symptoms emerged.

“Some of the recent cases … haven’t been tested for seven or eight days,” she said.

“If we don’t know about it, we can’t isolate it,” Ms Matson said.

Victoria had another 45 local COVID-19 cases on Wednesday. They included nine whose origin is yet to be determined.

There were also 28 that spent at least some time in the community while infectious.

State Health Minister Martin Foley said the trend was beginning to head in the right direction. However, mystery cases – especially those in the Newport and Altona cluster in Melbourne’s west – were still a concern.

“Whilst it’s heartening to see a reduction over the last couple of days, we know that numbers bounce around,” he said.

“It is the trend that the public health officials, in particular, frame their advice to government and their decisions around. And it’s our public health officials who still tell us there is a lot of work to do to make sure that, as we take vaccination rates up, we bring infection levels down.”

Victoria’s recent mystery cases are spread across several municipalities, mostly in Melbourne’s west. They include Hobsons Bay, Hume, Melton, Wyndham, Maribyrnong, Moreland, Monash and Glen Eira.

There are also concerns about continued wastewater alerts in areas with no recent positive virus cases. They include an industrial estate in Sunshine West, where health authorities are moving to door-to-door testing.

Similar wastewater alerts have been issued for Footscray, Seddon, West Footscray, South Kingsville and Spotswood in Melbourne’s west and Coburg, Coburg North, Fawkner, Hadfield, Preston, Reservoir and Thomastown in the north.

There were also five more cases in the regional town of Shepparton on Wednesday.

With that cluster hitting 50, the local health service estimates 17,000 people are isolating – a third of Shepparton’s population. There are more than 80 local exposure sites, including several supermarkets.

Health Minister Martin Foley said the state government was working with Victoria’s Emergency Management Commissioner, and Defence support would be provided if necessary.

“We’re well and truly engaged with not just Goulburn Valley Health, the council, the aged-care services, the school services, the civic support groups, the food supply groups,” he said in Melbourne.

“We’re working through all of those issues… to make sure that the people of Shepparton, and the Goulburn Valley more broadly, get all the support they need.

“It’s a challenge, but it’s a challenge I know that the people of Shepparton, and the people of Victoria, are up to.”

With more than 150 staff from Goulburn Valley Health isolating, Mr Foley said “a substantial” number of extra healthcare workers had been sent to Shepparton from health services in Melbourne and Bendigo.

Local residents have started doing food drives to support those affected by the outbreak.

The Shepparton outbreak has been genomically linked to an earlier outbreak at Glenroy in Melbourne’s outer north.

An infected patient from Shepparton has been identified as the index case that sparked an outbreak at the Royal Melbourne Hospital.

Eleven new exposure sites have also been listed between Geelong and Little River after six cases were connected to a household in Lara.

These cases are yet to be epidemiologically linked but are believed to be related to the Newport cluster.

Victoria has 36 COVID patients. There are nine in intensive care, including seven on ventilators.

The statewide lockdown is due to run until at least September 2.

-with AAP