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You may have heard the term "community transmission" being used in coronavirus news stories and updates from authorities.
It is used to describe the situation where a person is infected by the virus but they have not been overseas recently or been in recent contact with other confirmed cases.
The term basically means authorities are unable to trace the source of the infection.
"What that means is members of the community who are infected could be circulating that haven't been tagged as infected and that's where it becomes really, really problematic," University of Queensland virologist Kirsty Short said of community transmission.
"That's when it means we've missed cases of the virus and have transmission events happening that we haven't controlled."
The Department of Health reports that Australia does not have widespread community transmission of COVID-19.
It says "the majority of Australian confirmed cases acquired their infection overseas, including on board cruise ships or associated with recent travel to Europe or the Americas".
The below graph shows the rate of locally acquired transmissions of coronavirus in Australia where a contact has not been identified — indicating possible community transmission — in relation to overseas transmissions, locally acquired transmission with contact to a confirmed case, and confirmed cases where the transmission is still under investigation.
In Australia, the community transmission rate is just above 10 per cent.
But you won't find something if you're not looking for it
Until recently, only people who had been overseas or had contact with someone who had tested positive could get tested.
Testing criteria is only just starting to change in some parts of the country, and Catherine Bennett, the chair of epidemiology at Deakin University, said our high testing rate and low positive rate were a "red herring".
She said the current flattening of the curve could be misleading "if you're not testing the increasing number of people with symptoms in the community".
As several states expand testing criteria to include a broader cross-section of the community, any rise in the growth factor could be, in part, a result of more widespread testing.
"As we expand our testing we expect it to go up but that doesn't necessarily mean community cases are going up, it means that testing is broadening to capture them," Professor Bennett said.
Widespread community transmission means a loss of control
Dr Short said while imported cases of coronavirus were "relatively easy to control" with proper checks and tracing, community transmissions signalled a loss of control of the virus to varying degrees.
"It's a really concerning point. And certainly community transmission is not an ideal situation from an infection control perspective," she said.
What the experts are saying about coronavirus:
It suggested that once large-scale community transmission occurs, efforts to identify and trace individual cases should no longer be priority.
"Resources should instead be focused on monitoring the spread and characteristics of the virus, identifying and managing severe cases, preventing onward transmission of the virus, alleviating strains on healthcare services, informing the public, and reducing overall social and economic impact," the document says.
Another University of Queensland virologist, Ian Mackay, told newsGP that in countries like Iran, Italy and the US, "it seems the spread may have taken hold before preparations were made".
That meant those countries were playing catch-up on containing widespread community transmission, rather than preventing it from happening in the first place.
A case of community transmission in the US was first reported on February 26, while Australia's first confirmed community transmission was announced on March 2.
What you need to know about coronavirus:
Topics: covid-19, health, diseases-and-disorders, respiratory-diseases, australia