SINGAPORE, Dec 9 — A simpler, less invasive way to test for Covid-19 quickly that is close to the accuracy of a polymerase chain reaction (PCR) test in terms of correctly identifying infected individuals has been developed by scientists in Singapore.

The test requires only an individual’s saliva, rather than a throat or nasal swab. It is somewhat less accurate than a PCR test in terms of correctly identifying those who do not have the virus.

Unlike other saliva tests that must be done first thing in the morning after an extended period of fasting, the test can be used at any time of the day, the scientists said at a media conference on Wednesday (Dec 8). 

They said the test, which can be self-administered and is anticipated to have a low cost, had outperformed existing antigen rapid tests (ARTs) in early clinical testing and is "potentially game-changing".

The announcement by the team, comprising researchers from Duke-NUS Medical School, Singapore General Hospital (SGH) and National Cancer Centre Singapore (NCCS), and the National University of Singapore, comes two days after their findings were published in a peer-reviewed scientific journal.

Called Parallel Amplified Saliva Rapid Point-of-care Test (Pasport), it is, however, still perhaps three to six months away from being commercially available, the team said.

Dr Jenny Low, a senior consultant with the Department of Infectious Diseases at SGH, said there is still a need to carry out a “couple more clinical studies to validate the final commercial product”.

When asked if it will be able to detect the new Omicron variant, Associate Professor Melvin Chua, a clinician-scientist at the NCCS, responded that the team “does not see it as an issue”.  

In any case, Duke-NUS and SingHealth have filed intellectual property protection for the invention and are currently in talks with interested parties for licensing. 

However, Dr Soo Khee Chee, a Benjamin Sheares Professor in Academic Medicine at the SingHealth Duke-NUS Oncology Academic Clinical Programme, said the team has yet to receive approval for use from the Health Sciences Authority, though they are hoping to meet with the authority shortly. 

When it does become available, the researchers said that it will likely take about 15 minutes for the user to obtain his test result. 

In terms of cost, Dr Soo said he expects it to be similar to other test kits available on the market, but “vastly superior”.  

How does it compare?

The team’s clinical trials involved more than 100 participants between May and August this year.

According to their research, published on Monday in the journal Microchimica Acta, the trials found that Pasport’s sensitivity in detecting the virus was 97 per cent and its specificity 90.6 per cent, compared to PCR tests.

Sensitivity refers to the ability of the test to correctly identify patients who have the disease, while specificity refers to the ability to correctly identify patients who do not.  

The Ministry of Health said on its website that the PCR test — often referred to as the gold standard for diagnosing Covid-19 — has a sensitivity and specificity percentage of 99.5 per cent and 100 per cent respectively.

The scientists said it was not meaningful to compare the sensitivity and specificity levels of their invention with regular ARTs as they were citing their percentages in relation to PCR tests and not in absolute terms.

Up until now, saliva tests have not been rolled out on a large scale to detect the coronavirus as they were not considered reliable enough, said the researchers.

Pasport’s lead inventor, Dr Danny Tng, a medical officer at the Department of Infectious Diseases at SGH, said this is because the concentration of viral particles in saliva drops steeply after an individual eats or drinks. 

This means that conventional saliva antigen tests are usually only reliable when they are performed first thing in the morning, after an overnight fast and before breakfast or brushing teeth.

And while there are more accurate saliva PCR tests, they have their drawbacks too, said the researchers. 

PCR tests not only require trained personnel and laboratory infrastructure, but they also take about 24 hours before the results are known, said Dr Low.

As for swab-based ARTs, Dr Soo said that while they can be self-administered, it is not “the most pleasant experience”.  

Moreover, as it tends to elicit a sneeze, he said it puts swabbers at risk of potential infection if they are administering it on someone else. 

How it works

A solution was devised by the researchers to overcome the challenges of using saliva for rapid testing in the form of a two-stage process.

While Pasport uses nanoparticles to bind the virus like other ARTs, it also adds a second type of nanoparticle, said Dr Tng.

This has the effect of binding the first set of nanoparticles to “amplify the signal”, which increases Pasport’s accuracy in detecting the virus. 

Furthermore, it also allows saliva testing to be used at any time of the day because its sensitivity is not compromised even after eating or drinking. 

In terms of how it is used, Dr Tng demonstrated that the user only needs to put his drool into a receptacle, and then use a pipette to extract the saliva and transfer it to two sample wells on the test kit. 

Early diagnosis 

Dr Tng said testing is an indispensable tool in the management of Covid-19 cases. 

“A reliable and painless saliva antigen test that is affordable and convenient to perform would encourage more to be tested, and more frequent testing,” he said.  

Turning to Pasport’s potential applications, the researchers said that apart from serving as a screening tool for travellers at the airport or attendees of large scale events, there could be other useful contributions for managing Covid-19 cases here.

Professor Ooi Eng Eong, from the Duke-NUS Emerging Infectious Diseases Programme, said it could be used in conjunction with administering antiviral drugs. 

The Reuters news agency reported on Oct 7 that pharmaceutical company Merck had announced a supply and purchase agreement with Singapore that would ensure access to its experimental oral Covid-19 antiviral drug.

The drug Molnupiravir is designed to introduce errors into the genetic code of the coronavirus and would be the first oral antiviral medication for Covid-19.

“Like any other antiviral drug, the earlier you give it in the course of infection, the better the results. If you delay two to three days, then you're effectively losing the potency of what the antiviral drug can do,” said Prof Ooi.

As Pasport is as “good as a PCR test”, he said that it will enable general practitioners to administer a Covid-19 test on their patient and diagnose them on the spot without having to wait for laboratory results

“If we can give the drug early enough, then we're going to be able to prevent many people from going on to develop severe Covid,” said Prof Ooi. — TODAY