Evaluation of ECLIA antigen detection tests as screening methods for COVID-19 in comparison with molecular analysis.

BACKGROUND: Data from literature shows that antigen tests are rapid and helpful tools for diagnosis of COVID-19. AIM: This work aimed to evaluate the performances of the Elecsys SARS-CoV-2 Antigen test, in comparison to RT-qPCR, the gold standard. METHODS: A total of 110 swabs were tested; according to rRT-PCR, 76 were positive, and 34 were negative. The swabs were processed by Elecsys SARS CoV 2 Antigen assay (Roche Diagnostics GmbH, Mannheim, Germany), an electrochemiluminescence immunoassay (ECLIA). RESULTS: In a first evaluation, the overall sensitivity and specificity were 85% and 100%, respectively. It was noted that most of the discordant cases had cycle threshold (Ct) values > 28. Therefore, it was assumed a new measure to evaluate sensitivity and specificity, then samples with Ct values < 28 were selected. In this way, it was achieved a Ct < 28 sensitivity of 94%. The level of agreement between the two tests was 89. 1% with κ value of 0.77 for total data and 95.9% with κ value of 0.95 for samples with < 28 Ct. The antigen test performs well in the presence of high viral loads, whereas lower levels are missed. CONCLUSIONS: The comparison data obtained in this study support that this method seems a proper approach for rapid screening of patients with high SARS-CoV-2 viral load; however, the rate of sensitivity is highly Ct-dependent.

SARS-CoV-2 infection serology validation of different methods: Usefulness of IgA in the early phase of infection.

BACKGROUND AND AIMS: A novel coronavirus (SARS-CoV-2) was isolated from the respiratory samples of patients with pneumonia as showed by the sequence analysis of the virus genomes obtained in Wuhan, China. The antibody response to SARS-CoV-2 is not well understood yet, but the availability of sensitive and specific serological assays will be crucial for the early diagnosis of infection, for epidemiological studies and for defining the presence of neutralizing antibodies in response to a possible vaccine. MATERIALS AND METHODS: We tested and compared the performances of one chemiluminescent immunoassay (CLIA), two enzyme-linked immunosorbent assay (ELISA) and an electrochemiluminescence immunoassay (ECLIA). RESULTS: The ECLIA serological assay performed best and may be a valid screening method for SARS-COV-2 infection. The IgA detected by the ELISA assay might be a more reliable and stable early serological marker than IgM. Instead, IgGs, as expected, showed stable level after 10 days from symptoms onset. CONCLUSION: The ECLIA method could be used as screening test, considering both the excellent performance and the cost per single test; while ELISA assay for IgG and IgA, which are present at a higher level than IgM and last longer, might be used as confirmatory test.