Performance of the BinaxNOW coronavirus disease 2019 (COVID-19) Antigen Card test relative to the severe acute respiratory coronavirus virus 2 (SARS-CoV-2) real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay among symptomatic and asymptomatic healthcare employees

The sensitivity of the BinaxNOW coronavirus disease 2019 (COVID-19) Ag Card test (BinaxNOW) was 51.6% among asymptomatic healthcare employees relative to real-time reverse transcriptase polymerase chain reaction (rRT-PCR). The odds of a positive BinaxNOW test decreased as cycle threshold value increased. BinaxNOW could facilitate rapid detection and isolation of asymptomatically infected persons in some settings while rRT-PCR results are pending.

asymptomatic participants to determine the utility of BinaxNOW for detecting asymptomatic SARS-CoV-2 positive persons in an outbreak setting.
BinaxNOW is a rapid point-of-care lateral flow immunoassay that detects SARS-CoV-2 nucleocapsid protein antigen.The test was granted emergency use authorization (EUA) by the US Food and Drug Administration (FDA) on August 26, 2020, with intended use in persons with suspected COVID-19 within 7 days of symptom onset. 1 According to product information, the test achieves 97.1% sensitivity and 98.5% specificity when used within 7 days of symptom onset. 2 However, a statement issued by the FDA indicated that the test can be used off-label in asymptomatic persons if highly sensitive tests (eg, rRT-PCR tests) are not feasible or if turn-around times are prolonged. 2e report the diagnostic test characteristics of the BinaxNOW test relative to the PerkinElmer SARS-CoV-2 real-time RT-PCR test during a COVID-19 outbreak.

Employee testing procedure
During October 2-9, 2020, all employees providing patient care, except those who had tested positive for SARS-CoV-2 within the previous 90 days, were required by their employer to participate in widespread dual testing (BinaxNOW and rRT-PCR tests); testing for non-clinical staff was optional.Among ∼3,300 total employees (clinical and non-clinical), 2,339 participated in dual SARS-CoV-2 testing during the event.Employees who were tested also provided self-documented symptoms (ie, fever, cough, sore throat, dyspnea, chills, headache, muscle aches, vomiting, abdominal pain, diarrhea, or loss of taste or smell) and onset date of any symptom on laboratory reporting forms.Employees received testing at dedicated stations within the hospital through mobile teams deployed to hospital units or drive-through parking lot stations.

Laboratory methods
Two nasal swab samples were collected in random order from participating employees by trained hospital staff.Specimens for each test were collected by rotating the same swab at least 5 times, and for 15 seconds, inside both nares.
Univariate logistic regression analyses of BinaxNOW results relative to Ct values among rRT-PCR positive persons revealed that the odds of a positive antigen test decreased by 20% for each singlecycle increase in rRT-PCR Ct value (OR, 0.8; 95% CI, 0.7-0.9).The odds ratios were similar when stratified by symptom status (Supplementary Table S2 online).Among asymptomatic and symptomatic persons who tested SARS-CoV-2 positive by rRT-PCR, the Ct mean and Ct median were higher among persons who tested negative by BinaxNOW (Fig. 1; Supplemental Table S2

Discussion
We describe the test performance of the BinaxNOW test relative to the PerkinElmer rRT-PCR assay in the setting of a COVID-19 outbreak among hospital employees.Paired nasal swab testing of 2,339 employees revealed 152 persons who were positive for SARS-CoV-2 by rRT-PCR, 86 (56.6%) of whom were also positive by BinaxNOW.The diagnostic test sensitivity of BinaxNOW was 83.3% among symptomatic employees but only 51.6% in asymptomatic persons.Mean Ct values for persons who tested positive using BinaxNOW and rRT-PCR was lower (Ct mean = 21.4)than for persons who tested BinaxNOW-negative and rRT-PCRpositive (Ct mean = 32.0).This difference was observed among both symptomatic and asymptomatic employees.
Cycle threshold values cannot be used to determine viral load or infectivity in an individual, but on a population level, there is an inverse relationship between Ct value and the amount of genetic material present in specimens. 3These analyses demonstrated that asymptomatically infected persons with positive BinaxNOW tests had lower Ct values and, therefore, potentially higher viral loads, which might make them more likely to transmit the virus than asymptomatically infected persons who test negative by BinaxNOW.Despite the low sensitivity of the BinaxNOW test in asymptomatic persons, logistic regression analyses revealed that the sensitivity of the antigen card test improved among rRT-PCR-positive persons as Ct values decreased.Therefore, in an outbreak setting where interrupting transmission quickly is crucial, the benefit of using BinaxNOW could be the ability to rapidly screen and isolate infected persons who may be at greatest risk of transmitting SARS-CoV-2 while awaiting rRT-PCR results. 4his study has at least 2 limitations.First, symptom duration was not verified with the participants; thus, we were unable to assess the test performance of BinaxNOW within 7 days of symptom onset.This factor may have lowered the sensitivity of the test compared to the manufacturer's product information.Second, 29% of eligible employees did not participate in paired BinaxNOW and rRT-PCR testing.Because participants represented a convenience sample, the proportion of persons who were asymptomatic were likely overrepresented relative to the total number of employees because work exclusion and testing protocols were in place for symptomatic persons.Regardless, the impact of this convenience sampling on comparisons between BinaxNOW and rRT-PCR tests was likely minimal.
We report BinaxNOW test parameters relative to the PerkinElmer rRT-PCR assay for SARS-CoV-2 diagnosis during an outbreak of COVID-19 among acute-care hospital employees.The data suggest that, despite the lower sensitivity of the BinaxNOW COVID-19 Ag Card tests, these point-of-care tests could be strategically paired with rRT-PCR testing to immediately identify and isolate persons potentially at higher risk of transmitting the infection while rRT-PCR results are pending.

Fig 1 .
Fig 1. Distribution and median Ct values of SARS-CoV-2 rRT-PCR-positive samples from (A) symptomatic employees and (B) asymptomatic employees by BinaxNOW test result.
Ct values below 42 cycles for either N or Orf1 were considered positive for SARS-CoV-2.The second nasal sample was immediately placed into a BinaxNOW test card and run per label instructions by trained laboratory employees of hospital X. Hospital X reported antigen test results to the ADH.All paired samples were successfully tested.Test result data were combined into a single data set and stored on an ADH secure server.The diagnostic test parameters of the BinaxNOW test were calculated relative to the PerkinElmer rRT-PCR test, utilized as the reference standard, for all employees, symptomatic employees, and asymptomatic employees.Univariate logistic regression analyses were conducted to compare Ct values obtained from positive rRT-PCR tests with BinaxNOW test results.Ct values for N and Orf1 approximated one another (Pearson correlation coefficient, 0.99); therefore, only values for the N target are reported.Ct analyses were completed with SAS version 9.4 software (SAS Institute, Cary, NC).

Table 1 .
Comparison of Test ResultsFrom All Hospital X Employees, Symptomatic Employees, and Asymptomatic Employees at the Time of Sample Collection A person was considered symptomatic if they had at least 1 of the following: fever, cough, sore throat, dyspnea, chills, headache, muscle aches, vomiting, abdominal pain, diarrhea, loss of taste, or loss of smell.BinaxNOW COVID-19 Ag Card test.