Comparison Between Saliva, Swab Coronavirus Tests

From the start of the pandemic, researchers and clinicians have been searching for nasopharyngeal swab alternatives. Tests administered using these swabs are hard to scale up for mass testing, they put health workers in closer contact with individuals who may be infected, and they require more supplies. Saliva has been suggested as an easy and low-cost alternative. However, its accuracy and efficacy remain a point of conflict.

Trials of saliva-based tests have been carried out in the field but produced mixed results. These results only make it harder for saliva to be used in the existing testing framework as researchers don’t know under what conditions this method will be most useful.

Anne Wyllie, an epidemiologist at Yale School of Public Health, has studied saliva use as a genetic material source for the last 10 years. She recently investigated the role of saliva in coronavirus testing. To test the effectiveness of saliva, Wyllie and 50 of her colleagues conducted their own comparison and reported their findings in an analysis in the “New England Journal of Medicine”.

Of the 70 patients who were admitted to Yale-New Haven Hospital suspected of having the coronavirus, saliva samples collected contained more SARS-CoV-2 copies than found by swab samples. A high number of saliva samples was also found to be positive 10 days after the initial diagnosis. When used in group of 495 health-care workers, saliva tests discovered two more asymptomatic cases than swab tests did. This led the team to conclude that saliva specimens could potentially be used to help diagnose the SARS-CoV-2 infection.

It seems that in a controlled health-care setting, saliva can perform almost as well as nasopharyngeal swabs. However, the coronavirus has affected many communities around the world, with some of the hardest-hit communities being those that are underserved, poor or located in rural areas.

For instance, in French Guiana, about 300,000 confirmed coronavirus infections have been reported. A clinical trial was conducted by an epidemiologist from the Université de Guyane, Mathieu Nacher. The trial included a comparison between saliva and swabs for testing. Mobile field teams were deployed between July 27 and September 10 and gathered paired samples from 776 individuals across the coast.

Taking the testing directly into the field made it possible for researchers to gauge the efficacy of the screening tools in a real-world scenario. After collection, the samples were kept cool and processed within 24 hours. The paired samples underwent the same PCR test and extraction protocols to screen for three viral genes: RdRP, N and E.

The results from these tests showed that among the 776 individuals, 162 showed positive diagnoses from one of the two methods, with 76 receiving positive diagnoses from both swabs and saliva, 10 from only saliva and 76 from swabs alone. An estimated 39% of those who had the coronavirus were asymptomatic while the remaining 61% reported experiencing mild symptoms.

In general, as compared to nasopharyngeal swabs, saliva testing was found to be less sensitive. It should be noted that the results differed based on an individual’s viral load. A low load means that the CT number was high, and the two testing techniques disagreed more often. Additionally, saliva sensitivity when compared to swabs was only 24% in asymptomatic patients.

Researchers think the difference in performance between the two techniques also differed by the viral gene amplified. Despite lack of evidence, French health authorities officially announced that saliva testing could be used on symptomatic individuals in France and its territories.

Accurate testing is crucial in the biomedical field, and one company that you need to watch closely is CNS Pharmaceuticals Inc. (NASDAQ: CNSP). The company specializes in developing new drugs for the treatment of cancers affecting the central nervous system and the brain.

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