Could saliva tests be the way forward for COVID-19 screening?

Abu Dhabi: Since the start of the COVID-19 outbreak, testing for the coronavirus has been hailed as the one of the best ways to limit the spread of the disease.

While a number of different methods have been introduced to detect infection by Sars-CoV-2, the virus responsible for COVID-19, reverse transcription polymerase chain reaction (RT-PCR) tests via a nasopharyngeal swab have become the gold standard.

However, the slightly invasive nature of the nasopharyngeal swab - which involves the insertion of a portion of a 15-centimetre swab deep in the nose into the nasopharynx -is talked about by many of those undergoing the tests. So is saliva testing the way forward?

University study

At first, a study by the Mohammed Bin Rashid University of Health Sciences in Dubai collected and analysed saliva and nasal swabs from 401 adults who had visited the Khawaneej Health Center for a COVID-19 test. The results, published in the Infection and Drug Resistance Journal, showed that saliva can be used for viral detection with 70 per cent sensitivity and 95 per cent specificity, making it just as effective as the nasal swab.

Sajjad Naqvi, senior manager at the scientific office of Abu Dhabi’s leading COVID-19 testing laboratory, Pure Health, announced in September that the company has been working with the World Health Organisation on the new generation of saliva tests. Speaking on a radio show, Naqvi said that Pure Health checking the quality and proficiency of testing centres.

New saliva swab for COVID-19

Dr Youssef Idaghdour, assistant professor of Biology at the New York University Abu Dhabi, spoke to Gulf News about saliva testing. He has developed a new saliva swab COVID-19 testing protocol for the UAE, backed by Abu Dhabi’s health regulator, the Department of Health. Gulf News spoke to Dr Idaghdour to discuss the benefits and challenges of saliva testing.

What is the difference between the PCR test that is currently available and saliva testing?

The methodology used to detect the presence of Sars-CoV-2 remains the same i.e., the RT-PCR test conducted on the sample in the lab. What is different is the way in which the sample is collected. When the nasopharyngeal swab is used, the cell sample is collected from the nasopharyngeal tissue. Saliva testing would collect the sample from the mouth.

Are saliva tests as effective in detecting Sars-CoV-2 as nasopharyngeal swabs?

With all kinds of testing, false negatives are the main issue [that researchers hope to avoid]. With saliva testing, the rate of false negatives is the same as in testing through nasopharyngeal swabs, meaning that they are comparable. The virus can also be detected in saliva samples with 70 to 80 per cent sensitivity, as in nasopharyngeal samples. This is why many screening programmes are moving to saliva collection. For instance, the United States Food and Drug Administration has granted emergency use authorisation to Yale School of Public Health’s saliva test to detect COVID-19.

[Gulf News: The Yale saliva test, called Saliva Direct, requires no swab or collection device and uses spit from people suspected of having COVID-19. It also requires no extraction of RNA and can use several readily available reagents. A separate study at Yale also found that the coronavirus is stable in saliva for prolonged periods at warm temperatures, and that preservatives or special test tubes are not necessary when samples are collected.]

I’ve also added a few enhancements to the RT-PCR testing protocol, including a step known as pre-amplification, which amplifies the viral material in the sample. This really improves the sensitivity of the testing method, even by up to a 100 times. In addition, we’ve introduced a nanotechnology device, lab-on-a-chip, which can use really low volumes of sample for testing. This improves the precision of the test. These enhancements can be used to enhance any kind of RT-PCR testing, including saliva samples for COVID-19, and with them in place, it is possible to detect the coronavirus even in asymptomatic individuals.

For a person being tested, what is the major benefit of saliva testing?

The most obvious benefit is that saliva testing is painless, whereas a nasopharyngeal swab can be quite uncomfortable. The sample can be collected with a swab inserted into the mouth, or other kits can collect a sample of saliva as well. In fact, you can even introduce self-collection for saliva samples.

Could the manner of sample collection change?

This is another major advantage of saliva testing. With the nasopharyngeal swab, you need a trained healthcare worker to insert the swab, collect the sample, and ensure it is placed correctly into the transport medium. Otherwise, the [genetic material that is required to test for the virus], the RNA, can degrade. With saliva testing, there is the potential to collect raw saliva in tubes, because saliva has properties that preserve the RNA. So this could actually allow for self-collection of samples.

Also, there can be a lot of variation in testing results with nasopharyngeal swabs because they depend on the person collecting the sample. This variation can also lead to invalid tests. With saliva, it is much simpler to collect the sample, which therefore also allows for self-collection.

Is there any benefit to healthcare workers if saliva testing is introduced?

Of course, and this is mainly because self-collection of samples would reduce the healthcare workers’ risky exposure to patients. In turn, this would reduce the need for PPE required during the sample collection process.

Could we expect PCR tests conducted via saliva samples to be priced cheaper?

This depends on the testing authorities, but the cost of collecting saliva samples is cheaper. One reason for this is because collecting a saliva sample does not require the special tubes, swabs and chemicals needed to preserve coronavirus RNA obtained through a nasopharyngeal swab. In addition, if samples were self-collected, it would reduce the need for additional PPE used by healthcare workers during testing.

In addition, it is possible to skip a stage of testing in the laboratory, known as extraction. Extraction removes chemical reagents from the sample, but raw saliva can be preserved without reagents. So this eliminates the need for the special reagents, and therefore their cost.

Finally, with a very sensitive method of testing, it is possible to pool four samples to test at the same time. With the protocol I’ve developed, it is possible to test up to four samples, which can further reduce testing costs.

If saliva testing has so many benefits over the nasopharyngeal swan, why were they not introduced first?

This is a very good question. At the start of the COVID-19 outbreak, the disease was seen to be causing respiratory symptoms. So experts automatically suspected to find virus genetic material in the respiratory system tissues, [like the nasopharynx]. This was also in keeping with the way the disease progressed, as there are more virus particles in the nasopharynx than in the saliva in the early stages of the disease. It was only later that saliva tests were considered, and by then, governments had already rolled out a lot of resources to perform PCR tests using the nasopharyngeal swab.

Do you believe saliva testing will replace testing with nasopharyngeal swabs?

I actually do not see that happening, although I do believe there could soon be a small transition to testing through saliva samples.

It is also important to note that there is a difference between screenings and diagnostics, both of which require testing. When large swathes of people are being testing of COVID-19, they are mainly asymptomatic individuals, and it is not required to be as accurate in these tests as in diagnostics. With diagnostics, the individuals being tested are suspected of having COVID-19 and we need to use the best available methods to detect the coronavirus. In such a situation, both saliva testing and nasopharyngeal swabs can even be used in conjunction.

Do you believe that the introduction of saliva testing would increase the reach of COVID-19 screenings in the UAE?

The priority would be to introduce saliva testing using the extensive testing setup already rolled out by UAE health authorities, with as less disruption to the existing logistics as possible. With that being said, the painless nature of saliva testing would allow for children as young as three years to be screened.

[Gulf News: During mass screening drives, the UAE does not currently mandate testing via nasal swabs for children 12 years and younger. In addition, children younger than 12 years do not yet need to submit negative COVID-19 PCR test results in order to return to school premises.]