Studying temporal titre evolution of commercial SARS-CoV-2 assays reveals significant shortcomings of using BAU standardization for comparison.

BACKGROUND: Measuring specific anti-SARS-CoV-2 antibodies has become one of the main epidemiological tools to survey the ongoing SARS-CoV-2 pandemic, but also vaccination response. The WHO made available a set of well-characterized samples derived from recovered individuals to allow normalization between different quantitative anti-Spike assays to defined Binding Antibody Units (BAU). METHODS: To assess sero-responses longitudinally, a cohort of ninety-nine SARS-CoV-2 RT-PCR positive subjects was followed up together with forty-five vaccinees without previous infection but with two vaccinations. Sero-responses were evaluated using a total of six different assays: four measuring anti-Spike proteins (converted to BAU), one measuring anti-Nucleocapsid proteins and one SARS-CoV-2 surrogate virus neutralization. Both cohorts were evaluated using the Euroimmun Anti-SARS-CoV-2-ELISA anti-S1 IgG and the Roche Elecsys Anti-SARS-CoV-2 anti-S1 assay. RESULTS: In SARS-CoV-2-convalesce subjects, the BAU-sero-responses of Euroimmun Anti-SARS-CoV-2-ELISA anti-S1 IgG and Roche Elecsys Anti-SARS-CoV-2 anti-S1 peaked both at 47 (43-51) days, the first assay followed by a slow decay thereafter (> 208 days), while the second assay not presenting any decay within one year. Both assay values in BAUs are only equivalent a few months after infection, elsewhere correction factors up to 10 are necessary. In contrast, in infection-naive vaccinees the assays perform similarly. CONCLUSION: The results of our study suggest that the establishment of a protective correlate or vaccination booster recommendation based on different assays, although BAU-standardised, is still challenging. At the moment the characteristics of the available assays used are not related, and the BAU-standardisation is unable to correct for that.

Ectopic cervical thymic tissue: can imaging obviate biopsy and surgical removal?

Thymic tissue rests can be found all along the route of thymic descent from the neck into the anterior mediastinum and are frequently misinterpreted as pathological masses, which leads to biopsy or surgical removal. We present a case of ectopic thymic tissue in the neck and review the imaging characteristics of our patient and those found in the literature to determine if biopsy for this normal variation can be avoided. US findings of ectopic tissue reveal the exact tissue characteristics of normal thymus. The ectopic thymus may have an angulated configuration and mold over adjacent structures rather than displacing or invading them. If further verification is needed, T1-weighted MR images show homogeneous isointense or slightly hyperintense tissue compared with muscle and T2-weighted images show hyperintensity. The mass has the same structure as the normal thymus. We believe, on the basis of these findings, that one can confidently avoid the need for biopsy to prove that the discovered mass is ectopic thymus tissue.