There are three primary types of tests being deployed during this pandemic: RT-PCR, rapid antibody, and rapid antigen. PCR is a molecular or nucleic acid test, which determines if SARS-CoV-2, the coronavirus that causes COVID-19, is present in the sample. The sample is typically obtained via deep nasopharyngeal swab. However, doing less invasive sampling -- anterior nasal swab or saliva -- is gaining traction. PCR testing is the gold standard. It takes at least a day to get the results, and it can sometimes take a week or more. Note that these PCR tests, which require assay in a lab, are quite expensive -- typically costing over $100.
The rapid antibody test looks for antibodies to the coronavirus in a fingerstick of blood. Since these antibodies (IgM and IgG) do not appear in the blood until perhaps 1-2 weeks following the onset of symptoms, this test is only useful to know if some has had the disease and might now have some immunity. It is of virtually no use for diagnosing current illness.
The rapid antigen test will diagnose the disease as with PCR, and they provide results very quickly like antibody testing, but these antigen tests are typically not as sensitive as PCR since they do not amplify the viral DNA. Thus, there can be false negatives. However, they do have very high specificity. If you test positive, you are virtually certain to have COVID-19. Therefore, they are often used for screening applications. The Siemens Rapid Antigen Test, marketed by Narratek, has uniquely high sensitivity, at 96.72%, which means that there are very few false negatives. It is almost as accurate as the PCR tests; results are available within 15 minutes, and the price is a fraction of the cost of PCR testing. The delivered price is $13 per test for the minimum order quantity of 400 tests. There are discounts for larger orders.
SalivaClear meets all the key requirements for a test that should be universally used for COVID-19 diagnosis: easy, palatable, safe to administer, highly accurate, and fast results reporting. There is no need for a PPE-garbed medical tech. It is self administered. People just deposit some saliva in a tube that has a barcode on it. That barcoded number is linked to the person; the lab doesn't see any personal identifying information. The tubes are overnighted to the lab, where they are assayed via gold-standard RT-PCR, and the results are available about 12 hours after the samples are received.
Mirimus Labs uses the Yale SalivaDirect test [FDA EUA] but with pooling to provide the most cost effective program for screening and surveillance. See below for how it works. The price for this test is approximately one-fifth the typical price of the other RT-PCR tests. Pricing that low is enabled by Yale's free donation of its technology and by Mirimus's strategic pooling techology. SalivaClear is ideal for monitoring and detecting cases of COVID-19 in schools and other organizations, thereby preventing outbreaks.
Evidence on the Accuracy of Saliva Testing
Here are a couple of excerpts from this article in the LA Times:
"The saliva tests did a better job of detecting the virus formally known as SARS-CoV-2, the researchers found. In the first five days after diagnosis, 81% of the saliva tests came back positive, compared with 71% of the nasopharyngeal tests. A similar gap remained through the 10 day after diagnosis. In addition, the researchers detected more copies of the virus’ genetic material in patients’ saliva than in the samples taken from the back of their nasal cavities."
"To see how the tests stacked up among people with asymptomatic infections, the researchers recruited 495 healthcare workers with no signs of COVID-19 and gave them the saliva test. Thirteen of the tests came back positive. Among those 13 people, nine had given themselves nasal swabs on the same day, and only two of those tests came back positive. However, all 13 of the saliva tests were later confirmed by additional nasopharyngeal tests. The results were reported Friday in the New England Journal of Medicine."
The early data seem to show that for early diagnosis saliva testing might actually be more accurate than nasopharyngeal testing.