In Australia, more than 353,000 people have so far been tested for COVID-19 and more than 6,300 cases have been confirmed.
But Swinburne University's Professor Bruce Thompson said sometimes results can be incorrect and offer the wrong impression of safety.
"In some cases that we are seeing [globally], it's up to 20 per cent that's actually getting a false-negative result," the university's dean of health science told SBS News.
"So that's a bit of a problem because it might actually give someone a false sense of security."
A false-negative means the test tells you the result is negative, but it can actually be positive.
"We really want that to never happen, absolutely, but in terms of actually where we are with the technology, there will be a small number of false-negatives," Professor Thompson said.
"The test is very sensitive. That is, if the test is positive it is highly likely to be positive. However, if it is negative then there is a chance that the result is a false-negative result."
Why do false-negative tests occur?
In March, an Australian Department of Health spokesman told AAP the test being used in Australia was "very accurate".
The spokesman said false negative and positive results can occur "for reasons not associated with the test".
"For example, poor specimen quality is a common cause of false-negative results. It is best to collect specimens from patients with symptoms."
Professor Thompson added: "The reason for the higher false negatives mostly centre on a sampling error. The sample taken didn’t have the virus, or not enough virus, or it was contaminated somehow".
Writing in the earlier this month, Harlan Krumholz, a professor of medicine at Yale, said: "The problem may be with the test. Current coronavirus tests may have a particularly high rate of missing infections. The good news is that the tests appear to be highly specific: If your test comes back positive, it is almost certain you have the infection."
A rapid test to determine a person's immunity to COVID-19 has been developed in Australia. Source: AAP
The most common test to detect COVID-19 involves "a method capable of detecting virus particles that are generally present in respiratory secretions during the beginning of an infection," Professor Krumholz wrote.
"In the real world, though ... the virus can be missed. The best the Centers for Disease Control and Prevention can say is that if you test negative, 'you probably were not infected at the time your specimen was collected.' The key word there is 'probably'."
False-negative tests are commonplace in research - no test is ever perfect - and they have been occurring around the world in response to COVID-19.
"There are a lot of things that impact whether or not the test actually picks up the virus," Priya Sampathkumar, an infectious diseases specialist at Mayo Clinic in Minnesota, told AFP.
"It depends on how much virus the person is shedding [for example, through sneezing or coughing], how the test was collected and whether it was done appropriately by someone used to collecting these swabs, and then how long it sat in transport."
How many false-negative tests could be occurring?
Writing in the this month, Dr Sampathkumar warned even with high test sensitivity values, people could fall still through the cracks.
"In California, estimates say the rate of COVID-19 infection may exceed 50 per cent by mid-May 2020," she wrote.
"With a population of 40 million people, two million false-negative results would be expected in California with comprehensive testing. Even if only one per cent of the population was tested, 20,000 false-negative results would be expected."
Professor Thompson said it is important for tests to be highly sensitive and accurate, but they are only one measure of the virus.
He said a person may undergo a second test to double-check their result based on their likelihood of having the virus, symptoms, and depending on where the individual has travelled to.
"Even though we're testing more people, we're now starting to see the rate of rise of people testing positive is actually decreasing, which is really good," he said.
"So we're testing more people, we have a better understanding of what the incidents of this condition is in the community."
Professor Thompson said social distancing measures have been working in Australia and the federal government's Deputy Chief Medical Officer agrees the country is achieving test success.
Professor Paul Kelly said the low percentage of positive test outcomes indicates early detection, isolation and the reduced spread of COVID-19.
Warnings against faulty home tests
Federal Attorney-General Christian Porter has previously expressed concern about faulty testing kits coming from overseas which he said could be dangerous.
Australian Border Force officials identified a shipment of so-called 'home test kits'.
"We are well aware of it, we are trying to stop it as best we can at the borders by checking," Mr Porter said.
"For people who have any lack of certainty about the source of the test that they might have, or who are buying them online or through the post, don't do that," he said.
The home units were sent to Melbourne and Perth in March, originating from Hong Kong and China.
Home Affairs Minister Peter Dutton warned Australians against using the kits because inaccurate results could stop people from seeking treatment or discourage self-isolation when it is necessary.
Hospital staff test people outside the Tanunda War Memorial Hospital in the Barossa Valley, South Australia. Source: AAP
The Therapeutic Goods Administration, which regulates medicines, has ruled the tests are not approved.
Under the current testing system, the federal health department said doctors decide when to check suspected Australian cases.
People in high-risk settings where there are two or more individuals with symptoms such as fever and respiratory issues will be tested for COVID-19.
These environments included aged care centres, remote Aboriginal and Torres Strait Islander communities and correctional facilities.
Patients with symptoms who may have been overseas recently or on a cruise ship, work in aged care or the health sector, live in a high-risk area or who have come into contact with a known case will also be tested.
Testing criteria expands
The Federal Health Department said it regularly reviews testing criteria for COVID-19. But some states and territories will have different criteria based on their cases.
Victorian authorities said the testing of anyone with symptoms was unmanageable but the state has expanded testing to include people over 65 who are unwell and workers who come into close contact with the public, including teachers.
Professor Paul Kelly said this was an appropriate move with fewer overseas travellers now returning to Australian shores.
"This very much relates also to the local transmission component so that will be part of it," he said.
"Many states are also looking to increase surveillance through their fever clinics in emergency departments."
Australian university developing advanced test
Monash University has also taken a step forward in the fight against COVID-19 with more detailed tests in the works.
University researchers, together with Alfred Health, have been developing technology to find out which patients were still infectious with COVID-19, as opposed to just knowing who has been infected.
Monash Associate Professor Menno van Zelm said the test involved checking locals who have recovered from COVID-19, but also analysing the severity of the disease in overseas samples.
"It's really to determine how the immune response is generated to the virus but we really want to employ it to understand what is different between patients with a very mild form of disease to severe form of disease," he said.
"We'll hopefully be able to determine how long ago a patient has been exposed to the virus."
The blood test will help develop a more nuanced response to the disease and will detect who will be likely to catch COVID-19.
Professor Thompson said checking the body's reaction can also be useful as a different form of testing.
"So that's really interesting because you actually see the immune response, so you may not have the virus anymore because the body has killed it off, but you've actually generated what we call antibodies and we can actually see that you've already done it, so we know you've had the virus at some point."
Take note of official advice
"Your doctor will tell you if you should be tested. They will arrange for the test.
Generally, you will be tested if you develop fever or respiratory symptoms and meet at least one the following criteria:
- you have returned from overseas in the past 14 days
- you have been in close contact with someone diagnosed with COVID-19 in the past 14 days
- you travelled on a cruise ship (either passenger or crew) in the 14 days before developing symptoms
- you are a health care, aged care or residential care worker
- you have lived in an area where there is a higher risk of community transmission, as defined by the local public health unit
You should also be tested if you meet all of the following criteria:
- you are in hospital
- you have fever and serious respiratory symptoms
- there is no other clear cause of the symptoms"
People in Australia must stay at least 1.5 metres away from others and gatherings are limited to two people unless you are with your family or household.
If you believe you may have contracted the virus, call your doctor (don’t visit) or contact the national Coronavirus Health Information Hotline on 1800 020 080. If you are struggling to breathe or experiencing a medical emergency, call 000.
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