Could Spitting Into A Tube Be More Accurate Than Coronavirus Swab?

There are concerns the current swabbing test has produced false negative results. Is a saliva test any better?
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An at-home saliva test could be on the cards for detecting Covid-19 if a new trial goes to plan – and experts believe it could be more reliable in identifying cases of coronavirus than the existing swab test.

More than 14,000 people working in GP surgeries, universities and other frontline roles in Southampton have been recruited to trial the test and participants will be tested once a week for four weeks.

They will receive test results within 48 hours and details of those who test positive will be shared with the NHS Test and Trace Programme.

Why saliva could be better than swabbing

A saliva test is a lot less fiddly than its swab counterpart. At the moment, people can do postal swab tests at home or visit a drive-through testing facility.

The test involves inserting a swab into the nose and wiping it along the back of the throat, before it is packaged up and sent off to a lab to be tested.

There have been concerns that the swab test could be yielding a significant number of false negative results – meaning people are told they don’t have coronavirus when they actually do. Research from Bristol University and John Hopkins University has found up to 20% of swab tests return false negatives.

The new ‘spit’ test could be more sensitive than the swab tests currently being used, leading to better – and more trusted – results.

A study led by the Yale School of Public Health and conducted at Yale New Haven Hospital with 44 inpatients and 98 health care workers found saliva samples provided greater detection sensitivity and consistency throughout the course of an infection, compared to nasal swabs.

“Taken together, our findings demonstrate that saliva is a viable and more sensitive alternative to nasopharyngeal swabs and could enable at-home self-administered sample collection for accurate large-scale SARS-CoV-2 testing,” said study author Anne Wyllie back in April.

Professor Lawrence Young, an expert in molecular oncology and virologist at Warwick Medical School, tells HuffPost UK the Southampton trial is “exciting”.

“There have been several studies published over the past couple of months on testing for the virus in saliva samples,” he says. “I don’t think there have been thorough comparisons yet but everything coming out suggests that saliva is a much more reliable source of the virus [than swabbing].”

Prof Young believes the saliva test has the potential to be more accurate partly because it’s far easier to do. “What you’re doing is asking people to spit into tubes and to cough up whatever phlegm is in their throat, and that seems to be a much more reliable source of the virus,” he says. “It’s much easier than sticking a swab up into your nose or down into your throat.”

He points to studies from the US and Australia that suggest a greater accuracy from the swab tests – which have even identified positive cases among asymptomatic healthcare workers.

“Even though there hasn’t really been a large-scale comparison study yet between swabs and saliva, I think all the indications are that saliva is going to be a much more reliable and easy test in terms of sampling,” he says.

University of Chicago scientists found saliva-based tests were “just as accurate” as swabs. Using a system that measures how much of the virus is in a saliva sample, unlike swab tests that detect whether the virus is present or not, this method enables people who are asymptomatic (where they don’t have symptoms) or pre-symptomatic (where their symptoms haven’t developed yet) to be tested, too.

The theory goes that these people would show small amounts of the virus that a swab test might miss.

“It’s possible that people who have the virus but don’t show symptoms have a smaller amount of virus that wouldn’t show up on [swab] tests,” Jeremy Segal, an associate professor and pathologist at University of Chicago, said in a statement. “If they’re still able to spread the virus, being able to detect those people would be very important.”

People could also more easily do the saliva test from their own home without having to travel to test sites – thereby reducing the potential spread of the virus.

“It is definitely a positive step because it simplifies sample collection and also potentially results in a quicker time to [get the] result,” says Alexander Edwards, associate professor in Biomedical Technology at the University of Reading. “The faster the result, the easier it is to run things like track and trace, and to help people make informed decisions.

“Also, the more studies of testing methods, the better – we still need more information about the best way to test. This kind of testing technology is constantly improving and evolving, as we get smarter and slicker about detecting virus.”

Health secretary Matt Hancock said of the Southampton trial: “Saliva testing could potentially make it even easier for people to take coronavirus tests at home, without having to use swabs.

“This trial will also help us learn if routine, at-home testing could pick up cases of the virus earlier.”

The saliva test has been developed by UK company OptiGene, which has also developed a molecular diagnostic test for Covid-19 that provides results from swab tests within 20 minutes.

A quick and easy saliva test that told you whether you had coronavirus in 20 minutes could have a huge impact, says Prof Young.

“Just thinking about things like airports: if you can take saliva and very rapidly in 20 minutes get an answer, then I think that is going to be extremely useful in terms of managing some of the very difficult situations we find ourselves in, particularly in relation to the workplace and travel.”