Saliva swab test better in detecting Covid-19 than nasal swab test: Study

With the world nine months into the coronavirus pandemic, scientists are testing different methods of detecting the infection. Recently, a team of researchers demonstrated the efficacy of saliva-based tests that could give an effective result.

The new findings published in the New England Journal of Medicine also lend support to saliva-based tests. The researchers said in their study that saliva specimens can be an effective alternative to nasopharyngeal swab specimens that are being analysed by quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR).

Researchers compared saliva specimens with nasopharyngeal swab specimens concerning sensitivity in the detection of SARS-CoV-2 during infection.

Between March 23 and June 16, 2020, 321 Covid-19 inpatients at Yale-New Haven Hospital were identified as being eligible to enrol in the study and were approached by the clinical team.

Of these, 202 individuals were enrolled. Also, 495 asymptomatic healthcare workers were also enrolled in the active monitoring protocol.

The collection of nasopharyngeal and saliva samples was attempted every three days throughout their clinical course. The saliva samples were self-collected by the patients.

The researchers found that more SARS-CoV-2 RNA copies were detected in the saliva specimens than in the nasopharyngeal swab specimens.

Also, a higher percentage of saliva samples remained positive up to 10 days after the Covid-19 diagnosis.

At one to five days after diagnosis, 81 per cent of the saliva samples were positive, compared with 71 per cent of the nasopharyngeal swab specimens.

The level of SARS-CoV-2 RNA decreased after symptom onset in both saliva specimens and nasopharyngeal swab specimens.

During the clinical course, low variation was observed in the levels of SARS-CoV-2 RNA in the saliva specimens than in the nasopharyngeal swab specimens, the authors of the study noted.

The team said in a statement: “Collection of saliva samples by patients themselves negates the need for direct interaction between health care workers and patients. This interaction is a source of major testing bottlenecks and presents a risk of nosocomial infection.

“The collection of saliva samples by patients themselves also alleviates demands for supplies of swabs and personal protective equipment. Given the growing need for testing, our findings provide support for the potential of saliva specimens in the diagnosis of SARS-CoV-2 infection,” it concluded.