Coronavirus: ‘Painless’ saliva tests as effective as swabs in detecting silent carriers such as Trump, study finds

Faster, easier alternative to throat and nasal swabs could make mass testing schemes more feasible, scientist suggests

A man uses a saliva test in France during a police check on 29 September (Loic Venance/AFP via Getty Images)

“Painless” saliva tests for coronavirus are just as effective as the standard and more invasive swab test at identifying infection in asymptomatic carriers, a new study suggests.

As apparently evidenced in the case of Donald Trump, most people remain without symptoms during the first few days of infection. 

For this reason, some scientists have suggested mass testing programmes - such as Boris Johnson’s “operation moonshot” as a way to facilitate a return to some pre-pandemic behaviours while greatly reducing the spread of infection.

But the current polymerase chain reaction (PCR) swab test used in most countries requires too much manpower and resources to feasibly deliver such a programme, is often described as unpleasant to use, and has a turnaround time that renders it ineffective as a-near instant passport to crowded venues, workplaces and education settings.

However, the saliva test examined by researchers at Japan’s Hokkaido University in Japan delivers results within just 30 minutes, does not need to be carried out by health care workers, and does not require analysis by staff with scientific training.

While previous research on symptomatic Covid-19 patients found these saliva tests, known as RT-LAMP tests, to be less accurate than PCR swab tests, the new study published in the journal Clinical Infectious Diseases looked at its accuracy in identifying early, asymptomatic infection and found significantly different results.

The scientists tested and compared swab and saliva test samples of nearly 2,000 people in Japan who did not have Covid-19 symptoms.

The saliva test was found to have a very similar false positive rate to the traditional PCR test, correctly identifying infections in 83 to 97 per cent of participants with the virus and 77 to 93 per cent, respectively.

Both tests were able to identify those without the infection in more than 99.9 per cent of subjects, while the amount of virus - or viral loads - detected in the two tests were also similar.

“Saliva testing has significant logistic advantages over the commonly used nasopharyngeal swab testing,” said lead author Takanori Teshima. 

“Self-collection of saliva is painless for examinees, and more importantly, it eliminates the close contact with the examiners, reducing the risk of viral exposure.”

The results suggest that saliva tests might be “a useful alternative” to PCR testing, Prof Takanori added, “especially where diagnosis is required at the point of sample collection, like in sports venues or at airports”.

Researchers point to a limitation of the study that they did not follow up with clinical outcomes.

Nonetheless, they suggest that the results give good indication that mass screening using self-collected saliva and rapid RT-LAMP testing could provide easy, non-invasive, quick and relatively accurate results, with minimal risk of viral transmission to healthcare workers.

While the idea of mass testing has been met with scepticism in some quarters, Prof Takanori said: “Rapid detection of asymptomatic infected individuals will be critical for preventing Covid-19 outbreaks within communities and hospitals.”

In the UK, RT-LAMP tests were among those trialled at Heathrow Airport in a bid to get aviation off the ground, the results of which are being reviewed by the government.

Saliva tests have already been approved for use in Japanese airports and to reduce transmission in hospitals, while officials have discussed using them at the Tokyo Olympics as part of a mass testing regime.

And in the US, the use of PCR saliva tests are making headlines in mass testing efforts at the University of Illinois, which is conducting up to 20,000 tests a day in a bid to maintain normality on campus.