“What is happening in Victoria is a real concern and second wave is a real possibility if we don’t turn things around now,” Professor Booy said.
He said 95 per cent or more of Australians still had no immunity to COVID-19.
“This is a bug that is going to continue to cause trouble. When we start getting transmission rates indicating there is a community problem we need to pay attention.”
More than 1 million people live in the local government areas of Hume, Brimbank, Cardinia, Casey, Moreland and Darebin, which have been declared high-risk areas for transmission. Victorians have been urged to limit travel to those municipalities.
There are large family clusters of up to 14 people infected in the suburbs of Keilor Downs in Brimbank, Coburg in Moreland and Hallam in Casey, resulting in emergency testing sites being set up in those areas.
“Places like Cardinia, Hume or Brimbank are huge areas and the risk probably isn’t the same in all the suburbs, so it would be helpful for residents to have clear information,” Professor Allen Cheng, an epidemiologist and infectious disease doctor with Alfred Health, said.
On Wednesday morning, Victorian Health Minister Jenny Mikakos pledged to provide a suburb-by-suburb breakdown by the end of the day of infection rates in the six local government areas, but by the evening this was yet to be released.
A Department of Health and Human Services spokesman defended the delay and said data on infection rates was collected according to municipalities, rather than suburbs, and the state’s coronavirus detectives were still breaking down the information.
“It is a complex and lengthy process,” he said.
State Opposition Leader Michael O’Brien said the government must be more precise about which residents were most at risk, as there was confusion in the broader community about exactly where the hotspots were.
“I’m calling on [Premier] Daniel Andrews to stop using local government areas as the test on whether an area is a COVID hotspot. Please use towns, or postcodes or suburbs.”
Experts have also warned of a dangerous level of complacency that has led to some of those infected flouting social-distancing and quarantining measures and passing the virus on to an increasing number of people.
Ms Mikakos indicated the reproduction rate, a number aimed at calculating the rate of virus transmission based on modelling, had more than doubled from below one to 2.5 in the past week.
This means those infected with the virus are now each passing it on to an average of 2.5 people. The government has previously said the rate should always be below one.
“Once people carrying the virus stop taking precautions then it goes back towards the maximum transmission rate,” University of Melbourne epidemiologist Professor John Mathews said. “The only way drive that number down is with social distancing and lockdown procedures.”
Professor Cheng stressed that new cases emerging in hotspots were to be expected, but a rise in community infections across the state, where the source could not be traced, was troubling.
“Those high-risk areas are already under strict surveillance,” he said. “It’s the cases which we can’t trace the origins of which are most concerning.”
The source of eight cases reported in the past day remains under investigation. There have been 241 confirmed cases of coronavirus in Victoria that have been acquired through unknown transmission to date.
Burnet Institute epidemiologist Professor Michael Toole, who backed a suburb breakdown, said public health advice to marginalised communities in at-risk suburbs must be ramped up.
Community leaders and church leaders were paramount in reaching their communities, Professor Toole said.
“Some people in those communities needed person-to-person communication because there can be some suspicion about what governments are saying,” he said.
Professor Cheng said general practitioners working in suburbs deemed infection hotspots had a critical role in breaking down language barriers and providing their patients with updated advice.
Among the new cases are another three linked to a family cluster in Keilor Downs in Melbourne’s north-west, bringing that total 15.
A separate cluster of cases involving a family in Hallam in the south-eastern suburbs is connected with an outbreak among contractors at the Stamford Plaza quarantine hotel in the Melbourne CBD.
Three staff members from Hampstead Dental in Maidstone in Melbourne’s west have also tested positive for coronavirus. Another of the new cases involves a close social contact connected with a case at St Monica’s College Epping in Melbourne’s north, bringing that outbreak to two.
Professor Sutton said authorities wanted to keep the reproduction number below one.
“When it’s at two it means the active cases we have are doubling with each generation,” he said.
“We have seen the community transmission figures go from single figures [of cases] to above 10. But with the stabilisation in numbers in the last two days I expect that that will go back down. I absolutely hope that we can get it below one and drive those numbers back down to zero.”
The total number of coronavirus cases in Victoria is 1884. There are currently 141 active cases in Victoria.
Get our Morning & Evening Edition newsletters
The most important news, analysis and insights delivered to your inbox at the start and end of each day. Sign up here.
Melissa Cunningham is The Age’s health reporter.