Best COVID-19 test: Spit sample or nasal swab?

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In a new study, researchers found that saliva samples are a “preferable” indicator for COVID-19 infection than the deep nasal swabs now widely used.

They tested 44 inpatients and 98 health care workers and found that saliva samples taken from just inside the mouth provide greater detection sensitivity and consistency throughout the course of infection than the broadly recommended nasopharyngeal (NP) approach.

The study also found less variability in results with the self-sample collection of saliva.

The research was conducted by a team at Yale University.

Their 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.

The researchers also report that the saliva approach detected SARS-CoV-2 in two asymptomatic health care workers who had previously tested negative for the virus in an NP swab test.

Saliva testing may be especially useful due to its accuracy in identifying mild SARS-CoV-2 infections not detected with other methods, the researchers say.

More sensitive and consistent detection is expected to be critical in helping to assess when individuals can safely return to work and when local economies can reopen during the current pandemic.

Nasopharyngeal testing is considered the gold standard for detecting many upper respiratory tract pathogens.

The study notes that saliva is an appealing alternative to NP swabs because:

Collecting saliva is minimally invasive to patients.

Saliva samples can be reliably self-administered.

Saliva has exhibited comparable sensitivity to nasopharyngeal swabs in the detection of other respiratory pathogens.

The NP testing approach involves inserting a swab deep into the nostril and into the region of the pharynx. The swab is rotated to collect secretions, removed, then sent to a certified lab for analysis.

The US Food and Drug Administration on April 13 gave emergency use authorization for a saliva-based test for COVID-19.

The team says saliva testing requires fewer resources, personal protective equipment, and personnel than does nasopharyngeal swabbing.

Once tests and laboratories are validated for using saliva, this could be rapidly implemented and immediately resolve many of the resource and safety issues with SARS-CoV-2 testing.

The lead author of the study is Anne Wyllie, an associate research scientist at the Yale School of Public Health.

The study is currently available on the pre-print server medRxiv.

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