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Compared with PCR testing, Abbott's rapid antigen test picked up fewer cases in both symptomatic and asymptomatic individuals, researchers found.

Data from two community testing sites in Arizona showed sensitivity of 64% with the BinaxNOW test for specimens from symptomatic individuals and 35.8% in asymptomatic individuals, with real-time PCR testing as the gold-standard reference, reported Jessica Prince-Guerra, PhD, of the CDC, and colleagues.

When examining specimens positive for viral culture, the rapid antigen test did better but still short of perfect (92.6% sensitivity for symptomatic and 78.6% for asymptomatic individuals), the authors wrote in an early edition of the

However, they noted that in clinical context, real-time RT-PCR provides "the most sensitive assay to detect infection," and viral culture "is still an artificial system and is subject to limitations."

Data on rapid antigen testing performance has been sparse, though it has been in the spotlight before. According to media reports, a senior Trump administration official said the prior to the notorious Sept. 26 Rose Garden event introducing Amy Coney Barrett, who had just been nominated to the Supreme Court. Numerous individuals, including President Trump and first lady Melania Trump, subsequently developed COVID-19; all had tested negative with BinaxNOW as a condition for attending the event (except possibly the president himself, who later acknowledged he seldom underwent testing).

Indeed, Prince-Guerra and colleagues noted that while the FDA authorized a number of tests for use in symptomatic persons via emergency use authorization, "data are lacking on test performance in asymptomatic persons to inform expanded screening testing to rapidly identify and isolate infected persons."

The team examined specimens from two community testing sites in Pima County, Arizona, taken Nov. 3-17. Just over 3,400 people ages 10 and older provided samples for both RT-PCR and BinaxNOW testing. Of 299 individuals testing positive in the PCR assays, only 157 had positive results with the rapid antigen test. Specificity for the Abbott test was much better, however: among the 3,120 negative PCR tests, only four were positive with BinaxNow.

The researchers also attempted viral culture on 274 of 303 residual real-time RT-PCR specimens if either the PCR test or BinaxNOW result was positive. The investigators noted that the prevalence of positive RT-PCR test results in this population was "moderate" (8.7% overall, and 4.7% of asymptomatic participants).

Median participant age was 41, and over half were adults ages 18-49. Most were white. About one-quarter reported at least one COVID-19 symptom at the time of testing.

Because fewer than 10% of people in the study were genuinely infected, the Abbott test's negative predictive value was better than its sensitivity might suggest: 91.2% for symptomatic patients and 96.9% for those without symptoms.

Prince-Guerra and co-authors suggested that if rapid antigen testing was to be used in community testing strategies, such as schools, colleges, and congregate settings, serial testing might be used -- "which might improve test sensitivity in detecting infection," although this may cause logistical and personnel challenges.

The authors also recommended that, in people at higher risk for infection, negative antigen test results should be confirmed with nucleic acid amplification assays.

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