Epidemiologists and public health experts have warned Western Australia's low COVID-19 testing rates could mean there are undetected cases in the community.
WA's case numbers have fluctuated significantly in past weeks, recording zero cases on some days, while breaking into the 20s on others.
But one thing that has remained constant are the state's low testing rates.
Professor Linda Selvey, an epidemiologist at the University of Queensland, said WA's reliance on contact tracing meant it was even more important for people to get tested.
"If people even have the slightest symptoms, they should present for a COVID test," she said.
"Testing plays a really important role, particularly in the situation that Perth is in at the moment where you're relying heavily on contact tracing as a way to help control the cases."
There were long queues of people waiting to get tested at the Fiona Stanley Hospital COVID clinic last night after three cases emerged at Perth schools, with authorities urging anyone with symptoms to get tested.
Testing still important if cases undetected
Due to the sheer volume, contact tracing became less effective when case numbers surged, according to Professor Selvey.
"You don't actually need to detect absolutely every case, and we're never going to be able to do that," she said.
"We can do it with a certain level of slippage and still have a really good impact."
But even if some cases were not detected, she warned that testing rates still needed to remain high.
"As you move further on in the pandemic where it's not possible to do contact tracing anymore, it's still really important that people get the appropriate medical care," she said.
"Our testing rates have gone down considerably in Queensland following the huge spike in December, and probably at the moment not enough people are getting tested."
Professor Selvey said it was difficult to put an exact number on how much testing was required for it to be an effective measure.
Why is WA's testing rate so low?
WA's testing rate sits near the bottom of Australian states and territories, above only Tasmania.
Professor of International Health at Curtin University, Jaya Dantas, said the lack of a major outbreak in WA contributed significantly to why fewer people were getting tested compared to other states and territories.
"You have to remember those states have significant outbreaks. We don't," she said.
Professor Dantas said some people may not be getting tested because a high number of Omicron infections presented without any symptoms.
"Only a small number of Omicron cases get symptoms, and very few get serious symptoms and need to be hospitalised," she said.
"If people don't have any symptoms, they don't feel the need to go and get tested."
WA's vaccination rate also played a role in explaining the state's low testing rates, according to Professor Dantas.
"Because of our high vaccination rate, even if you're [only] double vaccinated, your chances of having no symptoms or mild symptoms is much higher," she said.
Clear messaging crucial, experts say
Experts said higher testing rates were critical to keeping WA's case numbers low.
Public Health Association of Australia CEO Professor Terry Slevin urged West Australians to "keep a lid on the virus" for as long as possible.
"Currently, Western Australia is not facing that challenge. Do your best to keep the virus suppressed as much as possible while the opportunity is available," he said.
Professor Slevin said the lack of cases in WA had created an environment where people did not feel the need to get tested.
"It's a question about the extent to which people in WA feel likely to be exposed," he said.
"The other question is if people can see a benefit in getting tested."
A lack of clear and consistent messaging could turn people away from taking up public health measures, according to Professor Slevin.
"The ongoing challenge with this pandemic is to provide clear, accessible, understandable, and consistent advice," he said.
"Try to explain it in a manner that people can see the clear benefit for them and the people around them.
"Of course, we need to take into account that circumstances with the pandemic continue to change, but a clear and simple message is fundamentally important."
How testing changes with more cases
Rapid antigen tests (RATs) are being recommended for routine surveillance in some states to reduce outbreaks in vulnerable settings, such as schools and aged care.
Currently, testing is used to stem outbreaks in WA before they grow out of control. But as, or if, case numbers surge, the role of testing will change.
Professor Dantas said RATs were effective for surveillance and reducing the load on clinics by allowing people to manage the virus themselves, while PCR tests allowed different strains to be identified.
"You want PCR testing because it's the gold standard, and at the same time PCR testing allows you to do genomic testing," she said.
"For any outbreak, genomic testing is really important. It allows you to know how to treat a patient that might be infected by the Delta variant, or if someone is infected with the Omicron variant.
"We can identify the variant this is predominant in the outbreak. In December, when we had the backpacker outbreak, it was the Delta strain.
"At present, we know that the dominant strain in WA is the Omicron strain."
