Saliva vs nasopharyngeal samples for COVID-19 testing

Two studies have found conflicting results when comparing the two methods of testing for COVID-19.

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31 August

• Saliva vs. nasopharyngeal samples for SARS-CoV-2 testing: studies find differing results.
• Victoria’s record one-day COVID-19 death toll includes historical cases.

• Can COVID-19 be reliably detected in saliva? Two studies have found conflicting results when comparing saliva with nasopharyngeal swabs as a means of testing for COVID-19.
  The first study, published in the Annals of Internal Medicine, was a prospective study involving 1939 high-risk individuals with few or no symptoms who presented for testing and gave both nasopharyngeal swabs and self-collected saliva samples. The samples were all tested for SARS-CoV-2 with RT-PCR.
  Thirty-four participants tested positive both on the nasopharyngeal and saliva samples. However 22 participants tested positive with the nasopharyngeal swab only, and 14 tested positive with saliva alone.
  The authors commented that saliva testing offers several advantages, in that it doesn’t require trained staff, can be done outside testing centers, and could be better tolerated in children.
  “Despite a lower estimated rate of detection relative to swab testing, saliva testing may be of particular benefit for remote, vulnerable, or challenging populations,” they wrote.
  A second study, published as a research letter in the New England Journal of Medicine, involved 70 people hospitalised with COVID-19 and compared saliva with nasopharyngeal swabs. This revealed that saliva had a higher number SARS-CoV-2 RNA copies than nasopharyngeal swabs, and the saliva samples were more likely to still be positive 10 days after the COVID-19 diagnosis.
  “These findings suggest that saliva specimens and nasopharyngeal swab specimens have at least similar sensitivity in the detection of SARS-CoV-2 during the course of hospitalization,” the authors wrote.
  They did a further study in 495 asymptomatic healthcare workers, 13 of whom tested positive with saliva samples. Nine of these also provided nasopharyngeal samples but seven of these were negative.
• On paper, Victoria has had its biggest one-day death toll from COVID-19, with 41 Victorians dying from the infection in the past 24 hours. However this figure actually included 33 aged care residents whose deaths in the weeks leading up to 27 August were only just reported to the health department on Sunday.
  Here are today’s confirmed COVID-19 infection figures from around Australia, to 9pm Sunday:
  National – 25,670, with 611 deaths.
  ACT – 113 (0)
  NSW – 4040 (7)
  NT – 33 (0)
  QLD – 1121 (4)
  SA – 463 (0)
  TAS – 230 (0)
  VIC – 19,015 (114)
  WA – 655 (0)