![]() The swabs were then tested according to the manufacturer’s instructions, and results were interpreted by 3 readers, blinded to the specimen variant and concentration, as positive, negative, or discordant (if not all 3 readers agreed). ![]() An additional specimen with only phosphate-buffered saline was used as a negative control. To do so, we initially created viral concentrations of 5.0 × 10 4, 5.0 × 10 5, 2.0 × 10 6, 5.0 × 10 6 copies/mL in phosphate-buffered saline, then immersed swabs from the BinaxNow kits into 50 µL of each dilution until the material was fully absorbed, as previously described. These dilutions were chosen to create concentrations both above and below previously reported limits of detection of the assay in a laboratory-based evaluation. We selected 2 Omicron variant specimens and 2 Delta variant specimens and produced serial dilutions to create swabs of 2.5 × 10 5, 1.0 × 10 5, 2.5 × 10 4, and 2.5 × 10 3 viral copies with each specimen. Positive AN swabs were stored in viral transport media and evaluated by viral load quantification and whole-genome sequencing. ![]() We recruited individuals testing positive for COVID-19 PCR at an academic medical center. We conducted a laboratory-based validation of the BinaxNow assay with anterior nasal (AN) swab specimens from participants in a study of coronavirus disease 2019 (COVID-19) virology. However, there are no published data on the validity of the assay with clinical specimens. Abbott, the manufacturer of the assay, has reported in a press release that the assay is predicted to detect the Omicron variant of SARS-CoV-2 infection. The initially identified lineage of the Omicron variant contains >50 mutations and deletions in comparison with ancestral lineages, including 4 mutations in the nucleocapsid gene, which is the target for the BinaxNow assay. In November 2021, the Omicron variant of SARS-CoV-2 was first reported in Southern Africa, and it quickly disseminated globally. Notably, test performance of chromatographic immunoassays, such as the BinaxNow, is dependent on specific viral antigens and may be impacted by changes in viral protein structure. The diagnostic validity of the assay has been demonstrated in laboratory-based and clinical settings, with a sensitivity ranging from approximately 50% to 90%, depending on disease stage and degree of symptom, and a specificity >99%, compared with laboratory-based polymerase chain reaction (PCR) assays. One such assay, the Abbott BinaxNow, has been recommended for in-home testing and implemented in public health screening campaigns. The US Centers for Disease Control and Prevention recommends rapid testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection as a key element of epidemic control. BinaxNow, diagnostic test, rapid antigen, SARS-CoV-2, viral load
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