For months now regional Victorian areas have relied on state data to know how many COVID-19 cases are reported in their area.
But despite the move toward rapid antigen testing, the numbers reported by local government areas still only include positive PCR results, leaving out half the state's cases.
Since mandatory self-reporting of rapid antigen tests was introduced on January 8, Victoria has seen an almost equal number of RATs to PCR tests.
But without localised figures including RAT results, it means the location of more than 18,503 new cases recorded on Tuesday through the home tests is unknown.
To get a better picture of their local figures, epidemiologist Tony Blakely said regions should be multiplying their daily case numbers by two.
"We know that roughly speaking, half the total cases are RAT and half the total cases are PCR at the moment," he said.
For regional areas like Ballarat, it means the 239 new cases recorded to midnight Monday were more likely close to 500.
Some cases not even reported
Lisa (not her real name) tested positive on a RAT in Mildura early this month but never reported her test to the government despite it making reporting mandatory.
With all the regular changes in rules and the stress of finding a test in the first place, she said reporting her case was not at the front of her mind.
"It wasn't on my radar," she said.
Lisa's nearest PCR testing clinic was more than an hour away and did not open until the next day and she was feeling too sick to drive.
By the time the government announced self-reporting, she said she had completed most of her isolation and reporting seemed pointless.
"I haven't spoken to anyone from the government. I definitely wouldn't be counted in the figures," she said.
Professor Blakely said Lisa was not alone, with thousands of cases likely going unreported because of asymptomatic people or people forgetting to report.
"The true number of infections out in the community is undoubtedly higher; I would put it at about four, five times higher than the sum of RAT tests and PCR at the moment.
Accurate reporting helpful
Regional areas like Ballarat have seen a steady rise in case numbers over recent days, with 824 active positive PCR cases in the region.
Professor Blakely said having an accurate idea of active cases could allow regional areas to react and create rules to protect the community.
"We'll have a bit more data with a combination of those RAT and PCR tests," he said.
"Assembling that data will help the Ballarats and the Milduras of this world to think about things like, should we bring the kids back for the first week of term or pause for one or two weeks?"
When reporting RAT results, people are asked to fill out their address, supplying location data to the government.
Professor Blakely said he believed the government would start reporting RAT results by region before the end of the week.
