Saliva testing for COVID-19 may work as well as, if not better than, current testing protocol, potentially saving the world time, money and lives.
A preprint of a potentially game-changing paper, which was released on April 22, suggested that saliva could be more sensitive to the COVID-19 virus, or SARS-CoV-2, than nasal swabs. The lead author on the paper, Anne Wyllie, associate research scientist in epidemiology, has spent the last six weeks working with saliva samples from healthcare workers and inpatients at Yale New Haven Health to investigate their potential use for testing. This study is a preprint, meaning it is a full draft of a study that has not yet undergone peer review.
“Saliva is a more consistent and easier test to take and always lower risk, and it saves time and PPE,” Wyllie said. “It could be really transformative for our testing efforts at the moment in a healthcare setting.”
The first testing kits used in the US for COVID-19 testing contained a nasopharyngeal (NP) test and an oropharyngeal (OP) test, according to Wyllie. The former requires a sample to be obtained from very far up one’s nose, and the latter requires a similar administration but instead reaches to the back of one’s throat, according to the Centers for Disease Control and Prevention.
After some time, it was discovered that the NP tests worked just as well as the OP tests. So in order to save time and money, most testing facilities switched to only the NP test, according to Wyllie. Saliva samples had not yet made it onto the testing scene.
“Nasopharyngeal swabs are routinely used to collect samples for influenza and other respiratory virus diagnosis,” Akiko Iwasaki, professor of immunobiology and molecular, cellular and developmental biology, and an author on the paper, wrote to the News in an email. “Saliva is rarely used for clinical testing of these viruses.”
The CDC does not list saliva as a viable option for running their test, but instead writes that “Nasopharyngeal specimen is the preferred choice for swab-based SARS-CoV-2 testing.”
Wyllie had done previous research on bacteria that can be detected in people’s saliva, so she thought it may be worth doing a study on SARS-CoV-2 to see if it was the case here.
According to the study, the 44 participants were all inpatients at YNHH with varying degrees of severe COVID-19 infection. From this group, a total of 121 samples were taken, including a combination of self-collected saliva samples and clinician-administered NP samples. For many patients, they had a pair of each kind of sample in order to carry out a direct, side-by-side comparison.
“Our results indicate that using saliva for SARS-CoV-2 detection is more sensitive and consistent than using nasopharyngeal swabs,” the study reports.
The study found that the saliva samples led to more accurate results, whereas the NP swabs, using the CDC’s SARS-CoV-2 detection test, would often result in false negatives. NP swabs were also found to yield contradictory results over extended periods of time.
According to Wyllie, there were many instances in which a person who is known to be infected with COVID-19 has an NP swab obtained and it comes back negative. And then the next day it yields a positive result. She said this flip-flopping can go on for days, showing severe inconsistencies.
“We’ve had a couple of cases where someone’s saliva has come out negative and their NP sample has come back positive. It is not perfect,” Wyllie said. “But if we flip it around the other side, the number of times saliva has been positive and the nasopharyngeal sample has been negative far outweighs the reverse.”
It is important that COVID-19 tests return as few false negatives as possible, according to Wyllie. She says that the World Health Organization’s criteria for declaring someone recovered is two negative tests. If an NP swab returns two false negatives, a person could be falsely informed that they are no longer infected.
“This saliva research is seminal,” said Camila Odio, a hospital physician at YNHH and an author on the paper. “They have already pre-published online and the paper is being reviewed by high-impact journals.”
This study is one of the first of its kind. A limitation of this investigation, however, is its sample size, and the paper notes the need for confirmation with larger samples. Wyllie explained that there are a few other studies being done in the U.S. and abroad on saliva testing, but not many are doing the same side-by-side comparison that her lab did.
“There was a big study that recently came out from China where they looked at something like 1,100 saliva samples, and they showed how useful it was, but they haven’t included any nasopharyngeal samples,” Wyllie said. “It’s all saliva.”
Although Wyllie’s paper has not yet been peer-reviewed, the results it contains could have a major impact on testing the U.S. and are already peaking the interest of others in the scientific community.
“Given the need for robust and widespread testing for SARS-CoV-2, any advance that expands the sample types and methods that can be used for SARS-CoV-2 testing is very helpful,” Ellen Foxman, an assistant professor of laboratory medicine and immunobiology, wrote the News in an email.
There is a clear need to increase screening in the U.S., and Wyllie said that continuing to test with NP swabs will not help with this issue. Currently, the country’s testing capacity is heavily limited by the materials that can be obtained to carry out testing.
“Saliva testing solves many problems,” Iwasaki said. “Saliva requires no swabs or viral transport media, both of which are in short supply. It also does not require a trained medical professional. NP swab collection requires training and PPE, and is not always reliable if the swabs are not collected properly.”
Transitioning to saliva samples will also increase the country’s test capacity because they could allow for at-home testing, according to Wyllie. She explained that people could just spit into a cup at home and mail it or drop it off at a testing center. On the other hand, NP swab collection is a very difficult process, and should not be done at home by anyone who is not a professional healthcare worker, according to Wyllie.
Wyllie’s study even investigated the accuracy of such at-home testing, with the use of healthcare workers as participants. They showed that self-collection of saliva samples at home were more sensitive to SARS-CoV-2 detection than clinician-administered NP tests.
“A nasopharyngeal swab collected with proper technique can be uncomfortable. Particularly for self-collection, it can be hard to collect a good sample,” Foxman said. “In contrast, saliva is much easier to collect, and the finding that the test for SARS-CoV-2 also works on saliva expands the possibilities for convenient testing.”
One of the most prominent benefits of using saliva samples is that this method will minimize the risk faced by healthcare workers doing COVID-19 testing. According to Wyllie, many individuals end up coughing or sneezing when they have the collection stick up their nose, which further exposes the healthcare worker to the virus. This would not be a risk with saliva testing.
“With our inpatients, we give them a cup. We say ‘When you wake up in the morning, let your saliva pool a little bit, spit into this cup, seal it up and leave it over there.’ And a healthcare worker can literally pop in, grab it and pop out,” Wyllie said. “No time and minimal contact.”
Despite the overwhelming potential benefits to using saliva samples, there are some challenges to making this transition. According to Wyllie, many labs currently carrying out testing, including the Clinical Virology Lab at YNHH, are not certified to use saliva samples. These labs will have to prove that they can do the tests with new samples.
“They’re going to have to get their side-by-side NP and saliva samples, figure out how to process them and show that they can process saliva and that it turns out the same way in their hands,” Wyllie said.
There will also need to be more data confirming Wyllie’s findings in order to get people on board, but, according to Wylie, the sooner people start using saliva testing, the better. She said that her work is ongoing, as they try to grow their dataset and make an even more convincing case.
Scientists at Yale have already received FDA approval for saliva testing, which Wyllie said is “a step in the right direction.” The paper expresses the urgent need to validate and implement saliva testing for COVID-19, as a result of its findings.
“I think we should be switching to saliva for testing immediately,” said Iwasaka.
Yale New Haven Hospital is located at 20 York St.