A healthcare worker collects a nasopharyngeal swab specimen to test a man for Coronavirus.

Nasopharyngeal swabbing — using a plastic stick to retrieve a sample from the back of your throat and nasal passage — is the current gold standard in collecting specimens to test for infections, including Coronavirus.

But the method causes discomfort, which contributes to why people avoid swabbing and reduces the ability to track the number of Covid-19 cases within a community.

Biologists have now found that samples collected through gargling are just as effective at detecting SARS-CoV-2.

In the new study, published in the journal Microbiology Spectrum, researchers compared gargling with swabbing the nose and throat in terms of the two methods' effectiveness for identifying Covid cases that show symptoms of disease.

The research involved testing samples from symptomatic participants through polymerase chain reaction, or PCR.

PCR tests aim to detect tiny amounts of genetic material by repeatedly copying (amplifying) whatever they can find. The tests are sensitive enough to detect viral material that's produced inside infected cells — including the RNA used by SARS-CoV-2, which is why PCR has become widely-used in labs to identify Coronavirus infection.

While the mix of saliva and mucus in your respiratory tract is called sputum, the liquid mixture produced from gargling (including mouthwash) is technically known as 'gargle lavage' (which comes from lava, Latin for 'to wash').

The study tested 80 people and detected 26 cases of Covid. In every single case where a sample tested positive from a nasopharyngeal swab, the virus was also detected from the gargle lavage.

Analysis of the PCR results revealed that levels of genetic material were higher in nasopharyngeal swab specimens than in gargle lavage samples, a difference that's greater when there was a higher concentration of virus.

One potential explanation for the observation is that SARS-CoV-2 infects the upper airways first — where nasal swabbing would be best for collection. Nonetheless, there was still plenty of virus for reliable detection from gargle samples.

According to Christof Hauck at the University of Konstanz in Germany, the cell biologist who led the study, gargling has the added advantage of being a simple method that doesn't require special tools or trained personnel.

"This sampling procedure can be conducted safely in a general practitioner's office without extra protective equipment for physicians' staff, as the patients themselves perform the sampling."

As nasal swabbing is not very pleasant, we were looking for an alternative," says Hauck, whose university carries out regular Covid surveillance by testing people twice a week. "Gargle lavage turned out to be highly accepted."

Hauck's study concludes that, compared to swabbing, the higher acceptability of gargling could lead people to be more willing to be tested repeatedly.

As an alternative to nasopharyngeal swab specimen, gargle lavage samples would accelerate diagnosis and ultimately help slow the spread of Covid-19.

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