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SalivaDirect COVID-19 test “really has potential” to speed diagnosis: FDA Deputy Commissioner

2020-08-21
photo courtesy of Gerd Altmann (geralt) via pixabay.com

 Anand Shah, MD, the Deputy Commissioner for Medical and Scientific Affairs at the Food and Drug Agency (FDA), said yesterday that a new test for COVID-19 called SalivaDirect “really has potential” to make testing more convenient and faster. He was speaking at a virtual press conference held Thursday morning and reported in Medpage Today this morning.

SalivaDirect, as its name implies, uses a sample of saliva from a person to test for the presence of RNA from the SARS-COV-2 virus. It requires only a sterile sample container. No ribonucleic acid (RNA) extraction step is needed to pull the virus’s genetic material from the sample. The test was created by the Yale School of Public Health in their Department of Epidemiology of Microbial Diseases. An Emergency Use Authorization was granted on August 15 by the FDA, and this news release describes the test.

The news release quotes Assistant Secretary for Health and COVID-19 Testing Coordinator Admiral Brett P. Giroir, M.D. as saying the test is an “innovation game changer that will reduce the demand for scarce testing resources.”

The test is not quite as sensitive as the currently standard nasopharyngeal swab, but it gives a big increase in convenience and reduced patient “discomfort” (gagging.) There is less time and fewer materials needed– due to skipping the RNA extraction step and the preservative in the vial. The test is inexpensive, with costs for all supplies running $1-$5. It is also validated for use with reagents obtained from multiple suppliers, making supply shortages less of a problem.

The test is described fully in this preprint published on MedRxiv on August 4. The article states that its detection limit is 6-12 SARS-CoV-2 copies per microliter. In direct comparison with the the Centers for Disease Control’s (CDC) test with saliva, it realized 93% sensitivity, missing 3 of 41 samples that tested positive otherwise– all three had extremely low levels of virus.

When compared with nasopharyngeal swabs tested from the same patient, saliva specimens tested with SalivaDirect showed 94% sensitivity and 100% specificity. A few specimens that tested negative with nasopharyngeal swabs were positive with saliva specimens, and this was confirmed with other tests– indicating that the nasopharyngeal swabs had missed a few truly positive patients.

The SalivaDirect test should be useful for outpatient testing and for asymptomatic people. It is thought to be less useful for sick patients in which blood and mucus can interfere with the test procedure due to the lack of RNA extraction.

If this test can be used as described for surveillance in asymptomatic people (a major shortcoming of the currently standard test, with its intrusive nature and the shortages of reagents) then it will surely be a big help in ramping up the number of examinations performed. Serial testing of people without symptoms is very important for making it possible to open up schools in particular.

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