Abstract
Many studies reported good performance of nasopharyngeal swab-based antigen tests for detecting SARS-CoV-2-positive individuals; however, studies independently evaluating the quality of antigen tests utilizing anterior nasal swabs or saliva swabs are still rare, although such tests are widely used for mass testing. In our study, sensitivities, specificities and predictive values of seven antigen tests for detection of SARS-CoV-2 (one using nasopharyngeal swabs, two using anterior nasal swabs and four using saliva) were evaluated. In a setting of a high-capacity testing center, nasopharyngeal swabs for quantitative PCR (qPCR) were taken and, at the same time, antigen testing was performed in accordance with manufacturers’ instructions for the respective tests. In samples where qPCR and antigen tests yielded different results, virus culture was performed to evaluate the presence of the viable virus. Sensitivities and specificities of individual tests were calculated using both qPCR and qPCR corrected for viability as the reference. In addition, calculations were also performed for data categorized according to the cycle threshold and symptomatic status. The test using nasopharyngeal swabs yielded the best results (sensitivity of 80.6% relative to PCR and 91.2% when corrected for viability) while none of the remaining tests (anterior nasal swab or saliva-based tests) came even close to the WHO criteria for overall sensitivity. Hence, we advise caution when using antigen tests with alternative sampling methods without independent validation.
Highlights
The identification of COVID-19 patients as early as possible after their infection is crucial for the successful management of the epidemic
The numbers of samples analyzed by individual rapid antigen tests (RATs) are detailed in Table 2, along with the test parameters calculated relative to the quantitative real-time PCR (qPCR) and for the same corrected for virus viability, as well as manufacturer-declared sensitivities and specificities (MDSe/Sp)
It is obvious that with the exception of the RAT using nasopharyngeal swabs, the performance of none of the tests met the criteria set by World Health Organization (WHO) and European Center for Disease Control (ECDC) [1,9]
Summary
The identification of COVID-19 patients as early as possible after their infection is crucial for the successful management of the epidemic. Numerous studies evaluated various RATs for SARS-CoV-2, with some reporting excellent results meeting or even exceeding the European Center for Disease Control (ECDC)/World Health Organization (WHO) criterion of 80% sensitivity, while others reported poor results. Such studies are reviewed, e.g., in [1,2,3]. Antigen tests are generally considered to be suitable for detecting the most infectious patients, i.e., those at the stage of the onset of symptoms and a few days before/after that. These are the patients with the highest viral loads, which correlates with generally lower cycle thresholds (Ct) in quantitative real-time PCR (qPCR) testing
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