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FDA Approves Rapid, Inexpensive 'Saliva Test' for Coronavirus--Accuracy & Advantages

FDA Approves Rapid, Inexpensive 'Saliva Test' for Coronavirus

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.

The new test, which is called SalivaDirect and was developed by researchers at the Yale School of Public Health, allows saliva samples to be collected in any sterile container. It is a much less invasive process than the nasal swabs currently used to test for the virus that causes Covid-19, but one that has so far yielded highly sensitive and similar results. The test, which also avoids a key step that has caused shortages of chemical reagents used in other tests, can test approximately 90 samples in fewer than three hours in a lab.

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%.

What about the Accuracy

“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.

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.

Advantages of saliva test

  1. Instead of relying on nasopharyngeal specimens, the new test uses saliva, which makes the sample collection non-invasive. 
  2. 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. 
  3. 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.
  4. Collecting nasopharyngeal samples can be uncomfortable to people, discouraging them from getting tested. The saliva test is likely to increase testing compliance.
  5. 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 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.

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