Best test for COVID-19: spit sample or nasal swab?

A nurse takes a swab at a COVID-19 drive-through testing station for NHS staff on March 30, 2020 in Chessington, UK. (Credit: Dan Kitwood/Getty Images)

Saliva samples are a “preferable” indicator for COVID-19 infection than the deep nasal swabs now widely used, according to a new study.

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

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

“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,” says first author Anne Wyllie, an associate research scientist at the Yale School of Public Health and a member of its Public Health Modeling Unit.

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 a 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.

The study has not been subject to peer review. The research results are currently available on the pre-print server medRxiv. The researchers called for the “immediate validation” of the results.

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 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. Researchers at RUCDR Infinite Biologics, a Rutgers University-backed biorepository. A qualified professional in a healthcare setting must conduct the approved test.

“With further validation, widespread use of saliva sampling could be transformative for public health efforts,” Wyllie says.

Saliva testing requires less resources, personal protective equipment, and personnel than does nasopharyngeal swabbing, the researcher says.

“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,” says Nathan Grubaugh, an assistant professor at the Yale School of Public Health and one of the senior authors of the study.

Source: Yale University