In what might turn out to be an important step in easy, inexpensive SARS-CoV-2 testing, a new rapid diagnostic test for novel coronavirus infection that uses saliva samples was granted an emergency use authorisation by the U.S. Food and Drug Administration (FDA) on August 15. It was submitted for authorisation by the FDA on July 14. The test uses a new method of processing saliva samples for testing coronavirus infection.
The test, called SalivaDirect, has high sensitivity, according to a preprint posted on medRxiv on August 4. According to the preprint, SalivaDirect test can detect when the number of virus copies in the saliva sample is as low as six-12 copies per microlitre. In contrast, testing nasopharyngeal swabs leads to false negative test results due to errors at the time of sample collection. The sensitivity was about 93%.
“Official data shows 88-94% [sensitivity]. If you assume 90% sensitivity, this is the best accuracy (sensitivity) of any saliva test,” Andy Slavitt, a former acting administrator of the Centers for Medicare and Medicaid Services in the Obama administration tweeted.
Collecting and testing saliva samples three steps — collecting saliva without preservative buffers, proteinase K treatment and heat inactivation, and dualplex RT-qPCR virus detection.
Evaluating the test
The test was developed by a team led by Nathan Grubaugh and Anne Wyllie of Yale School of Public Health in partnering with the National Basketball Association and National Basketball Players Association. The research team validated the efficacy of SalivaDirect in part by testing NBA players, coaches, and staff as they look to continue playing while ensuring the health of players and staff.
Prior to testing on NBA players, coaches and staff, Yale tested it on 44 inpatients and 98 health care workers. They found that saliva samples taken from just inside the mouth provided “greater detection sensitivity and consistency throughout the course of an infection than the broadly recommended nasopharyngeal approach”, according to a Yale release. The study also found less variability in results with the self-sample collection of saliva.
Open source protocol
Moreover, Yale has provided the testing protocol as an “open source” protocol, thus allowing laboratories in the U.S. to perform the tests. “Thus, SalivaDirect will be free to use by diagnostic labs. NGOs may apply for a licence. While the licence will be free, If you represent a for-profit organisation, we may issue a licence. The licence will be free, but we will want to negotiate how much you charge for the tests. We made this to be inexpensive, and we need those savings to be transferred to your customers.”
Advantages of saliva test
Instead of relying on nasopharyngeal specimens, the new test uses saliva, which makes the sample collection non-invasive. It also reduces the need for trained healthcare workers to collect the samples and reduces the risk of virus spread to healthcare workers at the time of sample collection. This is because collecting the sample from the nasopharyngeal region requires a swab to be inserted into the back of the nostrils, which very often causes irritation leading to sneezing and coughing, thus exposing healthcare workers from getting exposed to the virus.
Collecting nasopharyngeal samples can be uncomfortable to people, discouraging them from getting tested. The saliva test is likely to increase testing compliance.
“Saliva samples are a viable alternative to nasopharyngeal swabs and could allow for at-home, self-administered sample collection for accurate large-scale SARS-CoV-2 testing,” Dr. Wyllie said in a release.
The saliva sample can be collected in any sterile container. The diagnostic test also does not require the use of preservatives at sample collection, does not require specialised reagents or equipment for nucleic acid extraction. “The SalivaDirect methodology has been validated and authorised for use with different combinations of commonly used reagents and instruments, meaning the test could be used broadly in most high-complexity labs,” the FDA release says.
“The SalivaDirect test for rapid detection of SARS-CoV-2 is yet another testing innovation game changer that will reduce the demand for scarce testing resources,” Assistant Secretary for Health and COVID-19 Testing Coordinator Admiral Brett P. Giroir says in the FDA release.
The researchers validated SalivaDirect using several common and available reagents. The authors from the Yale School of Public Health, New Haven, Connecticut, U.S. claim that the test is inexpensive ($1.29-4.37 per sample). “SalivaDirect can help to realise large-scale testing of the general public to facilitate isolation and contact tracing of cases with the ultimate goal of preventing the spread of SARS-CoV-2,” they write.
In another preprint posted on medRxiv, the Yale School of Public Health researchers tested to know how long the virus was stable at different temperatures. They found that the virus particles were stable at 4 degree C, at 19 degree C and 30 degree C for “prolonged periods”. It was based on this result that the researchers did away with preservatives at the time of sample collection.
Experts welcome test
Even in the eight months of the pandemic, U.S. and other countries have struggled to test large number of people quickly and efficiently using a reliable test that is also inexpensive. The FDA emergency use authorisation has therefore been welcomed by public health experts.
“This could be one the first major game changers in fighting the pandemic,” Slavitt tweeted, who expects testing capacity to be expanded significantly. “Rarely am I this enthusiastic… They decided not to sell a specialised kit (so they didn’t have anyone run out). They are turning testing from a bespoke suit to a low-cost commodity.”
