In December 2019 the first reports of infections with the new SARS-CoV-2 coronavirus appeared in Wuhan, China. The virus spread rapidly around the world. SARS-CoV-2 is very contagious since one infected person passes the virus on to three healthy individuals. Different diagnostic methods are used for the detection of the virus; however, RT-PCR remains the gold standard. Samples are usually taken from easily accessible areas, for example, the nasopharyngeal area. Unfortunately, nasopharyngeal swabs are unpleasant for patients and present a risk for infection of healthcare workers. Lately, saliva samples are being considered for mass testing. The collection of saliva is non-invasive, affordable, and presents lower risk for healthcare workers. A study aimed to design a diagnostic method, based on RT-qPCR for the detection of the SARS-CoV-2 virus in differently collected saliva samples. The analytical sensitivity of the method is 3 copies of viral RNA/reaction (3000 copies/mL), meaning that it is within the wide range of analytical sensitivities of officially approved methods on the European Commission page. We also confirmed that the method can detect the virus in saliva before symptom onset. Afterward, the method was evaluated with differently collected saliva samples. We compared saliva samples collected with nylon and rayon swaps from the mouth and by passive drooling. Samples were paired with nasopharyngeal swabs, which were analysed at the National diagnostic centre using the officially approved PCR method. We established that the saliva sampling techniques significantly affect diagnostic sensitivity, but not diagnostic specificity. The best sensitivity was obtained for the saliva samples collected as passive drool (85 % for Cp < 30). Furthermore, passive drool saliva has the highest concordance with nasopharyngeal swabs (90 % for Cp < 30). The conclusion is that saliva collected by passive drool outperformed mouth swabs in a SARS-CoV-2 detection. In the end, we evaluated the clinical-diagnostic parameters of our method in comparison to the RT-qPCR methods from the National Institute of Chemistry (KI) and National Institute of Biology (NIB). We compared the results from passive drool saliva samples. We evaluated the effect of reaction volume sizes to test results. For our RT-qPCR method, smaller reaction volumes were used compared to methods from KI and NIB. We managed to confirm that bigger reaction volumes are more suitable, due to the higher rate of false-negative results in smaller volumes, which leads to lower diagnostic sensitivity.
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