Comparison of BinaxNOW TM and SARS-CoV-2 qRT-PCR detection of the Omicron Variant from Matched Anterior Nares Swabs

Abstract

The COVID-19 pandemic has increased the use of rapid antigen tests such as the Abbott BinaxNOWTM COVID-19 Antigen Self-Test. In winter of 2021-2022, the omicron variant surge made it quickly apparent that although rapid diagnostic tests (RDTs) are less sensitive than qRT-PCR, the accessibility, ease of use, and rapid read-outs of RDTs made them a sought after and often sold-out item at local suppliers. Here, we sought to qualify the BinaxNOWTM test for use in our university testing program as a method to rule-in positive or rule-out negative individuals quickly when they seek care at our priority qRT-PCR testing site. To perform this qualification study, we collected matched additional swabs from individuals attending this test site for standard of care qRT-PCR testing. All matched swabs were tested using the BinaxNOWTM RDT. Initially as part of a feasibility study, test period 1 (n=110) samples were put in cold storage prior to testing. In follow-on test period (n=209), we tested samples real-time at the test facility. Combined, 102 of 319 samples tested positive for SARS-CoV-2. All samples for which genome sequence could be collected were omicron (n=92). We observed a calculated sensitivity of 53.9%, specificity of 100%, a positive predictive value (PPV) of 100%, and a negative predictive value (NPV) of 82.2% for the BinaxNOWTM tests (n=319). Sensitivity improved (75.3%) by changing the qRT-PCR positivity threshold from a CT of 40 to a CT of 30. The ROC curve shows that for qRT-PCR positive CT values between 24-40, the BinaxNOWTM test is of limited value diagnostically. Our results suggest that RDT tests could be used in our setting to confirm SARS-CoV-2 infection in individuals with substantial viral load, but that a significant fraction of infected individuals would be missed if we used RDT tests exclusively to rule out infection.