Prospective study of three saliva qualitative antigen testing kits for the detection of SARS-CoV-2 among mainly symptomatic patients in Japan

Abstract

IntroductionRapid qualitative antigen testing has been widely used for the laboratory diagnosis of COVID-19 with nasopharyngeal samples. Saliva samples have been used as alternative samples, but the analytical performance of those samples for qualitative antigen testing has not been sufficiently evaluated. MethodsA prospective observational study evaluated the analytical performance of three In Vitro Diagnostics (IVD) approved COVID-19 rapid antigen detection kits for saliva between June 2022 and July 2022 in Japan using real-time reverse transcription polymerase chain reaction (RT-qPCR) as a reference. A nasopharyngeal sample and a saliva sample were simultaneously obtained, and RT-qPCR was performed. ResultsIn total, saliva samples and nasopharyngeal samples were collected from 471 individuals (RT-qPCR-positive, n = 145) for the analysis. Of these, 96.6% were symptomatic. The median copy numbers were 1.7 × 106 copies/mL for saliva samples and 1.2 × 108 copies/mL for nasopharyngeal samples (p < 0.001). Compared with the reference, the sensitivity and specificity were 44.8% and 99.7% for ImunoAce SARS-CoV-2 Saliva, 57.2% and 99.1% for Espline SARS-CoV-2 N, and 60.0% and 99.1% for QuickChaser Auto SARS-CoV-2, respectively. The sensitivities of all antigen testing kit were 100% for saliva samples with a high viral load (>107 copies/mL), whereas the sensitivities were <70% for high-viral-load nasopharyngeal samples (>107 copies/mL). ConclusionCOVID-19 rapid antigen detection kits with saliva showed high specificity, but the sensitivity varied among kits, and were also insufficient for the detection of symptomatic COVID-19 patients.