Explainer: what’s the new coronavirus saliva test, and how does it work?


Deborah Williamson, The Peter Doherty Institute for Infection and Immunity; Allen Cheng, Monash University, and Sharon Lewin, The Peter Doherty Institute for Infection and Immunity

A cornerstone of containing the COVID-19 pandemic is widespread testing to identify cases and prevent new outbreaks emerging. This strategy is known as “test, trace and isolate”.

The standard test so far has been the swab test, in which a swab goes up your nose and to the back of your throat.

But an alternative method of specimen collection, using saliva, is being evaluated in Victoria and other parts of the world. It may have some benefits, even though it’s not as accurate.




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Saliva testing can reduce risks for health workers

The gold standard for detecting SARS-CoV-2 (the coronavirus that causes COVID-19) is a polymerase chain reaction (PCR). This tests for the genetic material of the virus, and is performed most commonly on a swab taken from the nose and throat, or from sputum (mucus from the lungs) in unwell patients.

In Australia, more than 2.5 million of these tests have been carried out since the start of the pandemic, contributing significantly to the control of the virus.

Although a nasal and throat swab is the preferred specimen for detecting the virus, PCR testing on saliva has recently been suggested as an alternative method. Several studies demonstrate the feasibility of this approach, including one conducted at the Doherty Institute (where the lead author of this article works). It used the existing PCR test, but examined saliva instead of nasal samples.




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Keep your nose out of it: why saliva tests could offer a better alternative to nasal COVID-19 swabs


The use of saliva has several advantages:

  • it is easier and less uncomfortable to take saliva than a swab

  • it may reduce the risk to health-care workers if they do not need to collect the sample

  • it reduces the consumption of personal protective equipment (PPE) and swabs. This is particularly important in settings where these might be in short supply.

But it’s not as sensitive

However, a recent meta-analysis (not yet peer-reviewed) has shown detection from saliva is less sensitive than a nasal swab, with a lower concentration of virus in saliva compared to swabs. It’s important to remember, though, this data is preliminary and must be treated with caution.

Nonetheless, this means saliva testing is likely to miss some cases of COVID-19. This was also shown in our recent study, which compared saliva and nasal swabs in more than 600 adults presenting to a COVID-19 screening clinic.

Of 39 people who tested positive via nasal swab, 87% were positive on saliva. The amount of virus was less in saliva than in the nasal swab. This most likely explains why testing saliva missed the virus in the other 13% of cases.

The laboratory test itself is the same as the PCR tests conducted on nasal swabs, just using saliva as an alternative specimen type. However, Australian laboratories operate under strict quality frameworks. To use saliva as a diagnostic specimen, each laboratory must verify saliva specimens are acceptably accurate when compared to swabs. This is done by testing a bank of known positive and negative saliva specimens and comparing the results with swabs taken from the same patients.

When could saliva testing be used?

In theory, there are several settings where saliva testing could play a role in the diagnosis of COVID-19. These may include:

  • places with limited staff to collect swabs or where high numbers of tests are required

  • settings where swabs and PPE may be in critically short supply

  • some children and other people for whom a nasal swab is difficult.

The use of saliva testing at a population level has not been done anywhere in the world. However, a pilot study is under way in the United Kingdom to test 14,000 health workers. The US Food and Drug Administration recently issued an emergency approval for a diagnostic test that involves home-collected saliva samples.

In Australia, the Victorian government is also piloting the collection of saliva in limited circumstances, alongside traditional swabbing approaches. This is to evaluate whether saliva collection is a useful approach to further expanding the considerable swab-based community testing occurring in response to the current outbreaks in Melbourne.




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A saliva test may be better than no test at all

Undoubtedly, saliva testing is less sensitive than a nasal swab for COVID-19 detection. But in the midst of a public health crisis, there is a strong argument that, in some instances, a test with moderately reduced sensitivity is better than no test at all.

The use of laboratory testing in these huge volumes as a public health strategy has not been tried for previous infectious diseases outbreaks. This has required a scaling up of laboratory capacity far beyond its usual purpose of diagnosing infection for clinical care. In the current absence of a vaccine, widespread testing for COVID-19 is likely to occur for the foreseeable future, with periods of intense testing required to respond to local outbreaks that will inevitably arise.

In addition to swab-free specimens like saliva, testing innovations include self-collected swabs (which has also been tested in Australia), and the use of batch testing of specimens. These approaches could complement established testing methods and may provide additional back-up for population-level screening to ensure testing is readily available to all who need it.


This article is supported by the Judith Neilson Institute for Journalism and Ideas.The Conversation

Deborah Williamson, Professor of Microbiology, The Peter Doherty Institute for Infection and Immunity; Allen Cheng, Professor in Infectious Diseases Epidemiology, Monash University, and Sharon Lewin, Director, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne and Royal Melbourne Hospital and Consultant Physician, Department of Infectious Diseases, Alfred Hospital and Monash University, The Peter Doherty Institute for Infection and Immunity

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Keep your nose out of it: why saliva tests could offer a better alternative to nasal COVID-19 swabs



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Pingping Han, The University of Queensland

Saliva is one of our biggest foes in the COVID-19 pandemic, because of its role in spreading the virus. But it could be our friend too, because it potentially offers a way to diagnose the disease without using invasive nasal swabs.

Our research review, published in the journal Diagnostics, suggests saliva could offer a readily accessible diagnostic tool for detecting the presence of SARS-CoV-2, the virus that causes COVID-19, and might even be able to reveal whether someone’s immune system has already encountered it.

COVID-19 testing is a crucial part of the pandemic response, especially now countries are gradually lifting social distancing restrictions. This requires widespread, early, accurate and sensitive diagnosis of infected people, both with and without symptoms.

Our review looked at the results of three different studies, in Hong Kong, the nearby Chinese mainland city of Shenzhen, and Italy. All three studies found SARS-CoV-2 is indeed present in the saliva of COVID-19 patients (at rates of 87%, 91.6%, and 100% of patients, respectively). This suggests saliva is a potentially very useful source of specimens for detecting the virus.




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Saliva spreads the SARS-CoV-2 virus via breathing, coughing, sneezing, and conversation, which is why guidelines suggest we maintain a distance of at least 1.5 metres from one another. We also know SARS-CoV-2 can survive in tiny droplets of saliva in an experimental setting.


Author provided

Saliva is an attractive option for detecting SARS-CoV-2, compared with the current tests which involve taking swabs of mucus from the upper respiratory tract. Saliva is easy to access, which potentially makes the tests cheaper and less invasive. Saliva can hold up a mirror to our health, not just of our mouth but our whole body.

For this reason, saliva has already been widely investigated as a diagnostic tool for chronic systemic diseases, as well as for oral ailments such as periodontal disease and oral cancers. But less attention has been given to its potential usefulness in acute infectious diseases such as COVID-19, perhaps because researchers and clinicians don’t yet appreciate its full potential.

What a mouthful

When we get sick, much of the evidence is present in our saliva – from the germs themselves, to the antibodies and immune system proteins we use to fight them off. Saliva also contains genetic material and other cellular components of pathogens after we have broken them down (for the full biochemical breakdown of the weird and wonderful things in our saliva, see pages 51-61 of our review).


Author provided

Saliva is also hardy. It can be stored at –80℃ for several years with little degradation.

This means it would be relatively straightforward to track the progression of COVID-19 in individual patients, by collecting saliva at various times during the disease and recovery. Saliva tests from recovered patients could also tell us if they have encountered the disease for a second time, and how strong their immune response is.

However, there is no research yet available on using saliva to monitor immune responses. This will be well worth investigating, given the pressing need for a reliable and cost-effective way to monitor the population for immunity to COVID-19 as the outbreak continues.

Could saliva testing replace nasal swabs?

An ideal saliva test would be a disposable, off-the-shelf device that could be used at home by individuals, without exposing them or others to the risk of visiting a clinic.

One drawback with the research so far is that it has involved small numbers of patients (each of the three studies we reviewed involved no more than 25 people), and there is little published detail on exactly how these studies collected the saliva – whether from the mouth or throat, whether by spitting, drooling or swabbing, and whether collected by the patient or by a clinician.

Nevertheless, based on the modest amount of research done so far, saliva looks like a promising candidate for COVID-19 testing. More research is now needed, in larger groups of people, to learn more about how to confidently test for SARS-CoV-2 in the saliva of both symptomatic and non-symptomatic people.




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Earlier this month the US Food and Drug Administration approved the sale of saliva-based COVID-19 test kits that will allow people to collect their own samples and send them to a lab for analysis.

A reliable test would offer a cheaper, less invasive and potentially even more accurate way to detect the virus, which would also reduce the risk posed by routine COVID-19 checks to both patients and front-line medical professionals.The Conversation

Pingping Han, Postdoctoral Research Fellow, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.