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Pooled Saliva Tests Detect Covid-19 in Schools

Preparing classrooms for students return

Preparing classrooms in Des Moines, Iowa for return of students. (Phil Roeder, Flickr,

19 July 2021. Combining commercial saliva tests to speed detection of the SARS-CoV-2 virus in schools is shown as accurate as individual gold-standard nasal swab tests. Results of a study conducted in U.S. schools and colleges using real-world evidence from the SalivaClear test made by Mirimus Inc. appear in Saturday’s issue of the journal EClinicalMedicine.

Mirimus in Brooklyn, New York, designs SalivaClear for fast, regular, high-volume testing of populations, such as schools or work places. The SalivaClear test collects small saliva samples in tubes from individuals, on their own and without clinicians, to check for the presence of the SARS-CoV-2 virus responsible for Covid-19 infections. Samples from up to 24 individuals are then combined for lab testing. Any combined samples with negative results indicate all individuals in that pool are negative for SARS-CoV-2.

If analysis of the pool returns a positive response, saliva samples in that pool are reanalyzed in pairs. If reanalysis of any paired samples show a positive result, both of the individuals are retested with new samples to find if one or both are infected. Initial pool samples are returned in 24 hours, with paired and individual results returned in 12 and 6 hours, respectively, according to Mirimus.

Analysis of saliva samples are done by labs using the SalivaDirect technique designed at Yale University’s public health school. That technique uses reverse transcription-polymerase chain reaction, or RT-PCR, analysis to detect the presence of SARS-CoV-2 RNA in the samples, the same analytical method as nasopharyngeal swabs, the so-called gold standard for detecting SARS-CoV-2 done by clinicians. SalivaDetect received emergency authorization from the Food and Drug Administration in August 2020, and Mirmus’s labs are approved to analyze samples with the technique.

Similar results as nasal swabs at lower cost

The study analyzed SalivaClear results from 93 K-12 schools, 19 universities, and the Minnesota Timberwolves NBA basketball team, from August 2020 to January 2021, and compared the findings to RT-PCR tests from nasopharyngeal swabs. Samples were taken from students, teachers, faculty, and staff members. Researchers from Mirimus, Yale University, and participating institutions analyzed 253,406 self-collected saliva specimens, combined into 11,473 pools. The authors say SalivaDirect results were provided in 18 to 30 hours.

The results show analysis of pooled saliva samples correspond 100 percent to individual test results, indicating the pooling technique does not miss individual infection cases. Researchers also found 100 percent agreement between saliva and nasal swab tests, collected concurrently and sent to separate labs for analysis. Moreover, the team identified patterns of more infections over time, corresponding to holidays: Halloween, Christmas, and New Years. In one school, the findings detected a Covid-19 hot spot in its main office, where school staff found faulty HVAC and ventilation as the culprits. And when compared to selected community rates, school infections are generally lower than their surrounding communities.

“The positivity rates we measured in our study show that gathering in groups, such as holiday celebrations, significantly increases the transmission of Covid-19,” says Prem Premsrirut, CEO of Mirimus and senior author of the paper in a company statement released through Cision, “and while in-school transmission of Covid-19 appears to be relatively low, students and faculty are just as susceptible to Covid-19 infection as any population group. If, as we fear, many people remain unvaccinated, schools must continue to be extremely vigilant with mitigation protocols, including regular testing, in order to minimize exposure.”

In addition, the authors compared costs of pooled saliva tests compared to nasopharyngeal swabs. They found pooled saliva tests and analysis cost on average $10 per person, with additional paired reanalysis and retesting if required costing another $12.50 per person. Average costs of nasopharyngeal swab collection and RT-PCR analysis, however, range from $100 to $199 each in most cases, and $127 on average. Depending on numbers of students, faculty, and staff, cost savings from pooled saliva tests can quickly add up for individual schools and school districts.

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