According to a preprint study, saliva swabs are better than nasal swabs at detecting Omicron infections.
The heavily mutated Omicron variant has caused a sharp increase in COVID-19 cases across the world. Its rapid spread has further stressed the need for early detection of cases to control infections. However, the strain’s mutations make it harder to detect infections. Therefore, experts continue to debate over the best method for detecting Omicron cases. A recent preprint study has further added to the debate by demonstrating saliva swabs as more effective than nasal swabs.
The team of researchers recruited over 300 symptomatic, non-hospitalized patients who had presented to the Groote Schuur Hospital COVID testing center in Cape Town for COVID testing. They collected both nasal and saliva swabs from the participants and tested the samples via PCR. Moreover, the study researchers conducted whole-genome sequencing to classify the sample as Omicron or Delta.
According to the results, nasal swabs had a 100% accuracy rate for detecting the Delta variant. While saliva samples only had a 71% accuracy rate. Moreover, saliva samples had a 100% accuracy rate when detecting Omicron infections. However, nasal swabs only had an 86% positive percent agreement. Thus, suggesting that saliva samples perform better in detecting Omicron cases.
This is an important finding as the current standard of care for diagnosis using swabs of the nasal or nasopharyngeal mucosa may be suboptimal for the Omicron variant.
study author
Greater Viral Shedding in Saliva
The Omicron variant generally causes an upper respiratory infection. This is likely why there is higher viral shedding in the upper airway; thus, causing improved diagnostic performance of saliva samples. However, taking a saliva swab is not as easy as it sounds. According to study authors, participants must cough 3-5 times prior to taking a sample. Moreover, during the swabbing duration (approximately 30 seconds) one must swab the inside of their cheeks, above and below the tongue, on the gums and hard palate.
Participants should not have had any food, drink, tobacco or gum in the 30 minutes preceding saliva swab collection.
study author
Following the study, multiple people have taken to Twitter to announce the differences in their test results with the two swabs.
Reference:
Marais, Gert, et al. “Saliva Swabs Are the Preferred Sample for Omicron Detection.” 2021, doi:10.1101/2021.12.22.21268246.
