ABSTRACT
Massive testing is a cornerstone in efforts to effectively track infections and stop COVID-19 transmission, including places where good vaccination coverage has been achieved. 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 implementation in resource-limited settings. It is therefore important to develop testing protocols that facilitate implementation and are inexpensive, fast, and sufficiently sensitive. In this work, we optimized the composition of a buffer (PKTP) containing a protease, a detergent, and an RNase inhibitor, that is compatible with the RT-qPCR chemistry, allowing for direct testing of SARS-CoV-2 from saliva in an RNA extraction-independent manner. This buffer is compatible with heat-inactivation reducing the biohazard risk of handling the 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 (82.2% for the N1 and 84.4% for the N2 target, respectively) 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 reduce the number of PCR reactions per patient and further reduce overall costs while maintaining diagnostic standards in favor of massive testing.
