19 kovo, 2021

COVID-19 Diagnostics: How Do Saliva Tests Compare to Swabs?

Since the early days of the pandemic, clinicians and researchers have been looking for alternatives to nasopharyngeal swabs. While samples collected from swabs are considered the gold standard in terms of generating accurate results, these tests require more supplies, place health care workers in closer contact with potentially infected individuals, and are difficult to scale up for mass testing. Saliva has been put forth as a low-cost, easy alternative, but it’s efficacy and accuracy remain points of contention.                                                      

Even as large universities have begun rolling out ambitious, saliva-based initiatives on campuses across the United States, private companies looking to develop rapid, in-home diagnostic tests have moved away from such tools. Trials of saliva-based testing being deployed in the field have yielded mixed results, and it remains unknown under what conditions saliva is most useful or how best it can be rolled into the existing testing framework.

Anne Wyllie, an epidemiologist at the Yale School of Public Health, has studied the use of saliva as a source of genetic material for the last decade, and more recently has investigated saliva’s role in testing for COVID-19. Wyllie has been tracking the emergent literature during the pandemic to see how often saliva outperforms nasopharyngeal swabs. Across the almost 30 studies she has analyzed, “it’s almost half and half,” she says.

To test the efficacy of saliva herself, Wyllie and 50 colleagues did their own side-by-side comparison and recently authored a commentary in the New England Journal of Medicine in which they reported the findings.

Among 70 patients admitted to Yale-New Haven Hospital with suspected cases of COVID-19, saliva samples often contained more copies of SARS-CoV-2 than did swab samples, and a higher percentage of saliva samples were positive up to 10 days after the initial diagnosis. And when applied to 495 health care workers, saliva tests identified two more asymptomatic cases than swabs did, leading the team to conclude in their letter, “our findings provide support for the potential of saliva specimens in the diagnosis of SARS-CoV-2 infection.”

In controlled health care settings, at least, it seems that saliva can perform comparably to nasopharyngeal swabs. But COVID-19 is a global pandemic, and many of the hardest-hit communities are rural, poor, or otherwise underserved. And those conditions may influence just how well saliva-based tests work.

Source: The scientist (Amanda Heidt)