Comparison of SARS-COV-2 nasal antigen test to nasopharyngeal RT-PCR in mildly symptomatic patients

IntroductionCOVID 19 has been vastly spreading since December 2019 and the medical teams worldwide are doing their best to limit its spread. In the absence of a vaccine the best way to fight it is by detecting infected cases early and isolate them to prevent its spread. Therefore, a readily available, rapid, and cost-effective test with high specificity and sensitivity for early detection of COVID 19 is required. In this study, we are testing the diagnostic performance of a rapid antigen detection test in mildly symptomatic cases. (RADT). MethodsThe study included 4183 patients who were mildly symptomatic. A nasal sample for the rapid antigen test and a nasopharyngeal sample was taken from each patient. Statistical analysis was conducted to calculate the sensitivity, specificity, positive predictive value, negative predictive value and kappa coefficient of agreement. ResultsThe prevalence of COVID 19 in the study population was 17.5% (733/4183). The calculated sensitivity and specificity were 82.1% and 99.1% respectively. Kappas coefficient of agreement between the rapid antigen test and RT-PCR was 0.859 (p < 0.001). A stratified analysis was performed and it showed that the sensitivity of the test improved significantly with lowering the cutoff Ct value to 24. ConclusionThe results of the diagnostic assessment of nasal swabs in the RADT used in our study are promising regarding the potential benefit of using them as a screening tool in mildly symptomatic patients. The diagnostic ability was especially high in cases with high viral load. The rapid antigen test is intended to be used alongside RT-PCR and not replace it. RADT can be of benefit in reducing the use of PCR.