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Bustos-Garcia, Brandon; Garza-Manero, Sylvia; Cano-Dominguez, Nallely; Maria Lopez-Sanchez, Dulce; Salgado-Montes de Oca, Gonzalo; Salgado-Aguayo, Alfonso; Recillas-Targa, Felix; Avila-Rios, Santiago; Julian Valdes, Victor (2022)

DEVELOPMENT AND TESTING OF A LOW-COST INACTIVATION BUFFER THAT ALLOWS FOR DIRECT SARS-COV-2 DETECTION IN SALIVA

Vaccines (Basel) 10(5):
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Massive testing is a cornerstone in efforts to effectively track infections and stop COVID-19 transmission, including places with good vaccination coverage. However, SARS-CoV-2 testing by RT-qPCR requires specialized personnel, protection equipment, commercial kits, and dedicated facilities, which represent significant challenges for massive testing in resource-limited settings. It is therefore important to develop testing protocols that are inexpensive, fast, and sufficiently sensitive. Here, we optimized the composition of a buffer (PKTP), containing a protease, a detergent, and an RNase inhibitor, which is compatible with the RT-qPCR chemistry, allowing for direct SARS-CoV-2 detection from saliva without extracting RNA. PKTP is compatible with heat inactivation, reducing the biohazard risk of handling samples. We assessed the PKTP buffer performance in comparison to the RNA-extraction-based protocol of the US Centers for Disease Control and Prevention in saliva samples from 70 COVID-19 patients finding a good sensitivity (85.7% for the N1 and 87.1% for the N2 target) and correlations (R = 0.77, p < 0.001 for N1, and R = 0.78, p < 0.001 for N2). We also propose an auto-collection protocol for saliva samples and a multiplex reaction to minimize the PCR reaction number per patient and further reduce costs and processing time of several samples, while maintaining diagnostic standards in favor of massive testing.