New NSW COVID-19 cases likely 10 times higher than official figures: expert

| 14.08,20. 07:41 AM |

New NSW COVID-19 cases likely 10 times higher than official figures: expert

Despite testing more than 100,000 people a week, there are concerns some cases of COVID-19 are going undetected in NSW.(ABC News: Brendan Esposito)

The number of new COVID-19 cases in New South Wales each day is likely to be up to 10 times the figure reported by authorities, according to one epidemiologist, as fears about community transmission in the state grow.

University of Melbourne epidemiologist Tony Blakely made the estimation and said the presence of cases without a known source was "a good signal" actual case numbers were a lot higher.

"So, if they've got an average of 20 [cases per day] in the last week, that means that at any one point in time, there's about 200 other cases out there that we don't know about. Basically, 10 times the daily count," Professor Blakely said.

He said some of those cases would have an identifiable source, but others would be "mystery cases".

"If you've got a case that pops up and you can't trace it back to its source, and you assume that tracking has been done well … it means it's come from silent transmission," Professor Blakely said.

On Thursday, NSW reported 12 new cases of COVID-19, including three that were acquired locally without a known source.

In total, there were 380 cases in the state that were acquired locally, but the source had not been identified.

Leading epidemiologist Marylouise McLaws agreed NSW had some level of undiagnosed transmission of COVID-19, with at least one undiagnosed case for every diagnosed person.

"I am not sure I would put it as high as 200, but I accept the argument that for every diagnosed person, there is probably at least one other that we don't know about, or possibly two or three," Professor McLaws said.

"There are probably at least 20 cases that we are not aware of because it takes people a while to realise they are unwell and to get tested."

Professor Blakely said "silent transmitters" could be people who were infected with COVID-19, but were asymptomatic, as up to a third of all infections were.

"And then there are other people who are also silent transmitters who are so mildly symptomatic — they don't realise they have it," he said.

Both experts noted people who had COVID-19, but were pre-symptomatic, would be spreading the virus unknowingly before symptoms hit, contributing to community transmission.

"Eventually, a chain of transmission that is silent will end up with a case that's symptomatic. Someone … is going to get crook enough to present with symptoms and get tested," Professor Blakely said.

"It means the virus is circulating in the community."

Professor Blakely said after a couple of weeks of cases reappearing, it was "almost inevitable" some of those would be "mystery cases" without a known source.


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