Performance Characteristics of the Abbott BinaxNOW SARS-CoV-2 Antigen Test in Comparison to Real-Time Reverse Transcriptase PCR and Viral Culture in Community Testing Sites during November 2020

Abstract

Point-of-care antigen tests are an important tool for SARS-CoV-2 detection. Antigen tests are less sensitive than real-time reverse transcriptase PCR (rRT-PCR). Data on the performance of the BinaxNOW antigen test compared to rRT-PCR and viral culture by symptom and known exposure status, timing during disease, or exposure period and demographic variables are limited. During 3 to 17 November 2020, we collected paired upper respiratory swab specimens to test for SARS-CoV-2 by rRT-PCR and Abbott BinaxNOW antigen test at two community testing sites in Pima County, Arizona. We administered a questionnaire to capture symptoms, known exposure status, and previous SARS-CoV-2 test results. Specimens positive by either test were analyzed by viral culture. Previously we showed overall BinaxNOW sensitivity was 52.5%. Here, we showed BinaxNOW sensitivity increased to 65.7% among currently symptomatic individuals reporting a known exposure. BinaxNOW sensitivity was lower among participants with a known exposure and previously symptomatic (32.4%) or never symptomatic (47.1%) within 14 days of testing. Sensitivity was 71.1% in participants within a week of symptom onset. In participants with a known exposure, sensitivity was highest 8 to 10 days postexposure (75%). The positive predictive value for recovery of virus in cell culture was 56.7% for BinaxNOW-positive and 35.4% for rRT-PCR-positive specimens. Result reporting time was 2.5 h for BinaxNOW and 26 h for rRT-PCR. Point-of-care antigen tests have a shorter turnaround time than laboratory-based nucleic acid amplification tests, which allows for more rapid identification of infected individuals. Antigen test sensitivity limitations are important to consider when developing a testing program.

Keywords: Abbott BinaxNOW SARS-CoV-2 Ag Card; COVID-19; SARS-CoV-2; antigen test; viral culture.

FIG 1

Distribution of N1 cycle threshold values for samples positive by CDC 2019-nCoV rRT-PCR diagnostic panel, viral culture, and Abbott BinaxNOW COVID-19 antigen test by symptom and exposure groups. The distributions of N1 C_T values from rRT-PCR-positive specimens were compared for specimens analyzed with the CDC 2019-nCoV rRT-PCR diagnostic panel for detection of SARS-CoV-2 and were also analyzed by viral culture (n = 224). C_T values are represented on the y axis in descending order to indicate that lower C_T values represent larger amounts of RNA in the specimen. The median C_T values and interquartile range (IQR) for the groups are currently symptomatic and exposed, 24.6 (IQR, 20.4 to 31.6), and not exposed, 25.8 (IQR, 18.8 to 33.6); in previously symptomatic and exposed, 31.1 (IQR, 28.0 to 34.4), and not exposed, 30.0 (IQR, 27.7 to 34.3), and in never symptomatic and exposed, 27.2 (IQR, 19.3 to 34.1), and not exposed, 32.1 (IQR, 21.5 to 35.2). Colors indicate the antigen and culture test result of the specimen (red, culture positive/antigen positive; yellow, culture positive/antigen negative; gray, culture negative/antigen positive; black, culture negative/antigen negative).

FIG 2

Distribution of N1 C_T values for samples positive by CDC 2019-nCoV rRT-PCR diagnostic panel by viral culture and Abbott BinaxNOW COVID-19 antigen test by days since symptom onset or days postexposure. (A) Distribution of N1 C_T values for rRT-PCR-positive specimens tested by CDC 2019-nCoV rRT-PCR diagnostic panel by days postsymptom onset. Median N1 C_T values for 0 to 1 days postsymptom onset is 24.3; for day 2, 22.3; for day 3, 21.4; for day 4, 20.7; for day 5, 22.8; for day 6, 23.5; for day 7, 20.0; for days 8 to 13, 31.3; and days 14+, 35.2. (B) Distribution of N1 C_T values for rRT-PCR-positive specimens tested by CDC 2019-nCoV rRT-PCR diagnostic panel by days postexposure. Median N1 C_T values for 0 to 2 days postexposure is 29.2; for days 3 to 4, 22.5; for days 5 to 7, 22.1; for days 8 to 10, 25.0; and for days 11 to 14, 33.0. C_T values are represented on the y axis in descending order to indicate that lower C_T values represent larger amounts of RNA in the specimen.