These large clusters have quickly infiltrated at least four Melbourne families, resulted in the temporary closure of schools and have seen at least six local government areas – Hume, Casey, Brimbank, Moreland, Cardinia and Darebin – deemed dangerous hotbeds of transmission.
The two biggest family clusters, in the north-western suburb of Keilor Downs, and in Coburg in the north, have infected residents across at least five suburbs so far and directly led to the temporary closures of four Melbourne schools.
The clusters account for at least 25 cases with family members in the Hume, Brimbank, Moreland and Cardinia municipalities.
The Coburg family cluster has been linked to at least 14 cases, including at least four primary school aged children and extended family members in Broadmeadows, Coburg and Pakenham.
The Keilor Downs cluster has been traced back to at least 13 cases with teenagers and children among those infected.
The catalyst for spread has been attributed to family gatherings where social distancing measures were not upheld, authorities say.
A GP working across three medical clinics scattered across Melbourne has been linked to 12 cases, including members of his own family. The asymptomatic doctor worked at Lilydale Medical Clinic on June 11 and at both the Croydon Family Practice and Cedars Medical Clinic in Coburg on June 9.
A cluster originally linked back to a patient at Monash Health accounts for seven recent cases, including a healthcare worker, authorities have since declared it a family-based outbreak concentrated in Melbourne’s south-eastern suburbs.
The biggest cluster, however, has called into question the health department’s own handling of the matter,
Two large clusters among at least five security guards at the Stamford Plaza Hotel in Melbourne’s CBD and the Rydges on Swanston hotel in Carlton have accounted for 33 cases.
The security guards are contractors with a labour hire firm, contracted by the Department of Health and Human Services to monitor returned overseas travellers in quarantine at the hotels.
The source of these two outbreaks is the subject of an ongoing investigation, however, it is suspected a contractor may have picked it up from a traveller, before spreading the virus among colleagues through a lack of social distancing.
University of Melbourne professor of epidemiology Tony Blakely said there were a number of possible explanations behind Victoria’s jump in cases while other states have had few new infections, including mounting evidence of people flouting quarantine rules.
There may have been a super-spreader who unknowingly fuelled transmission within their own family, colleagues and the wider community, Professor Blakely said.
“Maybe one of those security guards might have been what we call a ‘super-spreader’ and he has passed it on to10 people and that was enough to tip the balance,” he said. “But we may never know this.”
Professor Blakely warned further outbreaks were likely and were a sign of the “suppression world” in which Victorians were living because the state had been unable to eliminate the virus to date.
Premier Daniel Andrews has blamed the surge in cases on families breaching restrictions, by visiting family members or going to work after testing positive to the deadly virus.
More than half of the new cases since the end of April had come from family-to-family transmission.
But Professor Blakely said the government must also “sort out its own quarantine practices” with family clusters linked to a spate of cases among security guards at quarantine hotels, where lax hygiene has been blamed for the outbreak.
“One hotel leaking out cases is maybe just bad luck, but two? This is not good,” he said. “This is a government run quarantine situation which is leaking out cases through security guards. It is interesting that Daniel Andrews focused on the people not behaving or sticking to quarantine, but actually there is just as much sorting out to do from the government side of how they are running their quarantine hotels.”
In the last three days alone, community transmission in Victoria has soared by 30 cases, the biggest jump recorded since the peak of the pandemic in April.
A case is classed as community transmission if the person who tested positive is not a returned overseas traveller or a close contact of an existing case.
UNSW Professor Mary-Louise McLaws, an infection-control expert and adviser to the World Health Organisation’s COVID-19 preparedness group, said people often assume their friends and family were not carrying the deadly virus because they knew and trusted them.
“We do seem to think if we know somebody, we like them, or we love them, they couldn’t possibly be a risk,” she said. “But in most cases they don’t know they have a deadly virus. My advice is always be respectful, but trust no one with your health. “
She said community spread in Victoria now had “velocity behind it” and it would be impossible to stop without re-enforcing severe restrictions.
“It has an exponential re-productiveness,” she said. “You’ve also got that hidden asymptomatic and pre-symptomatic group which could be anywhere between 20 to 30 per cent of people infected.
Melissa Cunningham is The Age’s health reporter.