According to a recent paper:

To validate the use of saliva for SARS-CoV-2 detection, we tested nasopharyngeal and saliva samples from confirmed COVID-19 patients and self-collected samples from healthcare workers on COVID-19 wards. When we compared SARS-CoV-2 detection from patient-matched nasopharyngeal and saliva samples, we found that saliva yielded greater detection sensitivity and consistency throughout the course of infection. Furthermore, we report less variability in
self-sample collection of saliva. Taken together, our findings demonstrate that saliva is a viable and more sensitive alternative to nasopharyngeal swabs and could enable at-home self-administered sample collection for accurate large-scale SARS-CoV-2 testing.

This made me wonder... why did countries initially presume that deep nasal swabs are the default route for detecting the virus? Why didn't we start out with basic saliva samples and then try out invasive sampling, rather than the other way around?

  • This article is a preprint and has not been certified by peer review. Also interesting statement within the paper "Although nasopharyngeal swabs are commonly used in respiratory virus diagnostics, they show relatively poor sensitivity for SARS-CoV-2 detection in early infection and are inconsistent during serial testing.(bolding added) – BobE Apr 23 '20 at 3:20
  • Some other recent (case) studies have even suggested SARS-CoV-2 persists even longer in the eyes (ocular fluids), so it should it be sampled from there. YMMV. – Fizz Apr 23 '20 at 3:48

From the paper you linked to

nasopharyngeal swabs are commonly used in respiratory virus diagnostics

So clearly it was preferred for Covid-19 because of the "received wisdom" from other respiratory virus illnesses. (To pick a random example, the 2005 WHO guidlines for avian influenza don't mention saliva samples, but various kinds of swabs and washes (for the upper respiratory tract): nasal swab, nasopharyngeal swab, nasopharyngeal aspirate, nasal wash, throat swab.)

If you want to ask why saliva sampling is not a method more widely used (instead of, or, in addition to nasopharyngeal swabs) in other respiratory virus diagnostics, modify your question according (incl. tag).


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