A leading epidemiologist has warned that as many as 60 per cent of the nation's current active COVID-19 cases could go undiagnosed, because of asymptomatic infections as well as social deterrents against getting tested.
According to the latest federal health data, there are just over 488,598 known active cases in Australia — more than half of them in New South Wales.
But Deakin University epidemiology chair Catherine Bennett said those cases potentially represented the tip of the iceberg, and that for every two known cases there could be another three that were not reflected in official health data.
She said that was due to a range of factors, including the fact that an estimated 30 per cent of cases were asymptomatic and might not know they were carrying the virus.
But she said that, despite frequent health messaging about the importance of getting tested, strict rules requiring close contacts of known cases to isolate could be deterring those with symptoms from getting tested.
"There have been people who have decided not to test because they didn't want that to happen to their household," she said.
"[If] you then have to tell your household contacts all to quarantine — even if some of those might have had an infection and not be very much at risk at all — it could be acting as a disincentive for people to get tested."
Professor Bennett said the 489,000 known active cases could represent just 40 per cent of the current caseload — meaning there could be as many as 750,000 people who currently have the virus but have not been diagnosed.
Another possible deterrent is the fear of missing work, highlighted by the case of an Adelaide woman who, despite testing positive, said she was recently quizzed by her employer about taking a sick day.
The woman, who did not wish to be identified out of fear of repercussions from her employer, said she began to feel "awful" last Monday and underwent a PCR test at Victoria Park on Wednesday.
She said while she had tested negative, the person administering the test had only "put the swab in my nose for about two seconds" and that two subsequent rapid antigen tests (RATs) had returned positive results.
The woman said she contacted her employer on Sunday telling them she had tested positive, but they replied suggesting she undergo another PCR and asked where she believed she caught COVID from.
"I felt like that's none of their business," she said.
"[Their attitude was] 'we don't really believe you and want you back at work because it's quite inconvenient'."
University of South Australia epidemiologist Adrian Esterman said it was "shocking" to hear of such a case.
"That company is putting its own profits before the health of the community," he said.
"We've got places like South Korea, you've got Vietnam which has got hundreds of thousands of cases a day — and you may think, 'So what, because most of them only get mild illness?'
"But there's a small percentage who get very sick and die — and even fit, healthy people get very sick and die — and 10 per cent of them are going to get long COVID."
Professor Esterman said it was plausible that there were "at least a million" active cases in Australia at the moment, a significant proportion of which were likely to remain unrecorded.
"Thirty per cent of people who get infected are asymptomatic," he said.
"On top of that, there are people who use a rapid antigen test, test positive, and they don't notify the authorities.
"On top of that, there's people who refuse or won't get tested for social reasons, in that they don't want to curb their social lives and they don't want to miss work. So that's why you've probably got at least double the number of [known] active cases."
