So far more than 100 people in Victoria have had a saliva test for coronavirus after the state became the first in Australia to roll out the more pleasant, albeit slightly less exact, option.
It's not intended to replace nasal or throat swabbing Victorian Premier Daniel Andrews says, it's simply an extra line of defence in the fight to contain outbreaks.
Saliva testing was introduced after the Victorian Deputy Chief Health Officer revealed 30 per cent of returning Victorians in hotel quarantine had refused swab testing.
Right now saliva testing is only offered to those in hotel quarantine or residents in Melbourne hotspots, but could it potentially be rolled out more widely in the future?
Let's breakdown the new 'spit test'.
How do you do a saliva test?
You collect saliva in your mouth for a minute or two and then spit it into a jar.
That jar is then sent to a lab where the saliva is tested.
Recent research has found there was a three-hour gap between the saliva collection at the Royal Melbourne clinic and the lab testing.
How do the saliva and swab tests work?
There are two main ways to test for the SARS-CoV-2, the virus that causes COVID-19.
The most reliable is the reverse transcriptase Polymerase Chain Reaction (PCR) test which can pick up the genetic information of the virus (the RNA) when someone is actively infected.
Both nasal swabs and saliva samples undergo PCR testing.
Serology testing uses blood samples to analyse whether someone has COVID-19 antibodies. If they do, it means they've had the virus at some point in the past.
Serology testing has limitations as it doesn't allow for any direct action, in fact it would show a negative result even if you had COVID-19 at the time of testing.
For this reason serology testing is only being used in special circumstances.
How reliable is the saliva test?
TLDR: Nasal and throat swabbing remains the gold standard of testing, but a saliva test is better than nothing.
The Peter Doherty Institute for Infection and Immunity in Melbourne put saliva samples to the test in March and April by taking specimens from 622 patients at the COVID-19 screening clinic at the Royal Melbourne Hospital.
All 622 people had nasal/throat swabs, and 522 of them also provided saliva. The nasal/throat swabs returned 39 positive results and the saliva samples returned 33.
Therefore, the institute says the saliva test has a sensitivity rate of around 87 per cent, so out of 100 tests, 13 will be false negatives.
A sensitivity rating basically tells us how few viral particles the test needs to pick up to give a positive result.
Microbiology professor Stephen Turner from Monash University has this to say about the "threshold of detection":
"So you need a certain amount of virus in a sample to get a signal. With a swab test, the amount of virus you need is a lot lower, so it's more sensitive.
"Whereas with saliva, you need a lot more virus to get a signal."
It's impossible to give a definitive sensitivity rating for the nasal/throat swab (basically because there's nothing better to test it against) but it's more than 90 per cent, Professor Turner says.
Swab tests still produce what Dr Norman Swan calls a "significant minority" of false negatives, with one report by the Johns Hopkins University in the US suggesting the chance could be greater than one in five.
Why is the saliva test less sensitive?
Saliva is a complex mix of fluids containing water, electrolytes, proteins and enzymes and all of these dilute the viral genetic material of COVID-19.
"The other thing is, saliva is where the virus ends up before it's transmitted, it's not where it's growing, it's not as direct a test of infection," Professor Turner says.
Could it give a false positive result?
The Doherty Institute says there is no chance a saliva test could return a positive result if the person is COVID-19 negative.
The institute's researchers tested saliva specimens from 50 patients who returned negative nasal/throat swabs.
The saliva tests didn't return any false positives, and in fact, picked up one positive result that the swab testing had missed.
The researchers said this might reflect the inconsistencies that can arise when a swab isn't taken properly by a nurse or doctor.
"If the result is positive — we can trust the saliva test. But if it comes back negative and there's still some clinical suspicion that that person might have been exposed to the virus, they may then choose to get a nasal swab," University of Queensland virologist Ian Mackay says.
What are the advantages of the saliva test?
If you have already had a COVID-19 test, you will know that it's not a pleasant experience and spitting into a jar is far more preferable.
"For little kids, which seems to be one of the target audiences here, a saliva test is a much more attractive and agreeable form of collection", Dr Mackay says.
It's not just children though, those in vulnerable categories including the elderly, particularly those with dementia, or some people with disabilities may prefer this method of detection.
In turn, our testing will hopefully broaden, Professor Turner says.
"We might get more tests done and a broader range of the population, because people who might not have gone to get a test because they don't like the idea of having a swab down their throat might now be more amenable," he says.
And because you can do a saliva test at home, the potential for exposure at a COVID-19 clinic is eliminated, benefiting both patients and health care workers.
It's also worth noting that saliva samples are sent to the exact same laboratories as nose/throat swabs so we're not changing the kind of testing, just the sample.
Why now?
In late June the Doherty Institute received an anonymous donation of $1 million to boost its COVID-19 research.
Half of that donation was spread between three projects, one being the investigation of saliva as an alternative diagnostic specimen for COVID-19.
The Doherty Institute wouldn't comment on whether the roll-out of saliva testing was already scheduled for June or was moved forward to combat the rising spread of community transmission.
The Victorian Department of Health told the ABC the saliva test was introduced to investigate just how widespread community transmission was and authorities want to test its ability to be scaled up before offering it to any more people.
Just last week the UK announced a four-week trial of at-home saliva testing and in May the US Food and Drug Administration permitted one lab to start selling at-home saliva collection kits.
What do the experts think?
The benefits of saliva testing far outweigh the disadvantages, Professor Turner says.
Dr Mackay agrees and wants to assure people there is no need to have any hesitations about taking a saliva test.
He says rolling out saliva testing in the outbreak hotspots was wise and it has the added benefit of giving researchers more data to examine.
"We're in this great position where we don't have a lot of cases so we don't have the same urgency. We can afford to do things like this and expand the knowledge and that can be leveraged by other places around the world as well."
Director of the Doherty Institute Sharon Lewin says it would be a "perfect outcome" if people no longer had to leave their home for a COVID-19 test.
The Doherty says there will be ongoing analysis of the saliva testing in Melbourne and further research will "hopefully" be published.
NSW has not ruled out introducing the saliva test if the need arises for greater testing in the future.
https://news.google.com/__i/rss/rd/articles/CBMiW2h0dHBzOi8vd3d3LmFiYy5uZXQuYXUvbmV3cy9oZWFsdGgvMjAyMC0wNy0wMS9jb3JvbmF2aXJ1cy1zYWxpdmEtdGVzdGluZy1leHBsYWluZWQvMTI0MDY5MTLSASdodHRwczovL2FtcC5hYmMubmV0LmF1L2FydGljbGUvMTI0MDY5MTI?oc=5
2020-06-30 20:35:00Z
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