Evaluation of Abbott BinaxNOW Rapid Antigen Test for SARS-CoV-2 Infection at Two Community-based Testing Sites

Pima County, Arizona, November 3-17, 2020

Jessica L. Prince-Guerra, PhD; Olivia Almendares, MSPH; Leisha D. Nolen, MD, PhD; Jayleen K. L. Gunn, PhD; Ariella P. Dale, PhD; Sean A. Buono, PhD; Molly Deutsch-Feldman, PhD; Suganthi Suppiah, PhD; LiJuan Hao, MD; Yan Zeng, MS; Valerie A. Stevens; Kristen Knipe, MS; Justine Pompey, PhD; Christine Atherstone, PhD; David P. Bui, PhD; Tracy Powell, PhD; Azaibi Tamin, PhD; Jennifer L. Harcourt, PhD; Patricia L. Shewmaker, PhD; Magdalena Medrzycki, PhD; Phili Wong, MS; Shilpi Jain, PhD; Alexandra Tejada-Strop, MS; Shannon Rogers, MS; Brian Emery; Houping Wang, PhD; Marla Petway, MPH; Caitlin Bohannon, PhD; Jennifer M. Folster, PhD; Adam MacNeil, PhD; Reynolds Salerno, PhD; Wendi Kuhnert-Tallman, PhD; Jacqueline E. Tate, PhD; Natalie J. Thornburg, PhD; Hannah L. Kirking, MD; Khalilullah Sheiban, MD; Julie Kudrna, MPA; Theresa Cullen, MD; Kenneth K. Komatsu, MPH; Julie M. Villanueva, PhD; Dale A. Rose, PhD; John C. Neatherlin, MPH; Mark Anderson, MD; Paul A. Rota, PhD; Margaret A. Honein, PhD; William A. Bower, MD

Disclosures

Morbidity and Mortality Weekly Report. 2021;70(3):100-105. 

In This Article

Discussion

In this evaluation, using real-time RT-PCR as the standard, the sensitivity of the BinaxNOW antigen test was lower among specimens from asymptomatic persons (35.8%) than among specimens from symptomatic persons (64.2%). Specificity (99.8%–100%) was high in specimens from both asymptomatic and symptomatic groups. The prevalence of having SARS-CoV-2 real-time RT-PCR positive test results in this population was moderate (8.7% overall; 4.7% for asymptomatic participants); administering the test in a lower prevalence setting will likely result in a lower PPV.†† Among 11 participants with antigen-negative, real-time RT-PCR–positive specimens with positive viral culture, five were symptomatic and six asymptomatic. Some antigen-negative, real-time RT-PCR–positive specimens possibly could represent noninfectious viral particles, but some might also represent infectious virus not detected by the antigen test. In a clinical context, real-time RT-PCR provides the most sensitive assay to detect infection. Viral culture, although more biologically relevant than real-time RT-PCR, is still an artificial system and is subject to limitations. Numerous biological (e.g., individual antibody status and specific sequence of the virus) and environmental (e.g., storage conditions and number of freeze-thaw cycles) variables can affect the sensitivity and outcome of viral culture. Despite the limitations of interpreting culture-negative specimens, a positive viral culture is strong evidence for the presence of infectious virus. The performance of the BinaxNOW antigen test compared with real-time RT-PCR was better for those specimens with positive viral culture than for all specimens, with a sensitivity of 92.6% for specimens from symptomatic persons and 78.6% for those from asymptomatic persons. The results of the current evaluation differ from those of an evaluation of the BinaxNOW antigen test in a community screening setting in San Francisco,[7] which found a BinaxNOW antigen test overall sensitivity of 89.0% among specimens from all 3,302 participants, regardless of the Ct value of the real-time RT-PCR–positive specimens.

The findings in this investigation are subject to at least five limitations. First, anterior nasal swabs were used for BinaxNOW antigen testing, but NP swabs were used for real-time RT-PCR testing, which might have contributed to increased detection for the real-time RT-PCR assay.[8] Second, participants might have inadvertently reported common nonspecific symptoms as COVID-19–compatible symptoms. Third, this investigation evaluated the BinaxNOW antigen test, and results presented here cannot be generalized to other FDA-authorized SARS-CoV-2 antigen tests. Fourth, the BinaxNOW antigen test characteristics might be different depending on whether an individual had previously tested positive. Finally, many factors might limit the ability to culture virus from a specimen, and the inability to detect culturable virus should not be interpreted to mean that a person is not infectious.

Public health departments are implementing various strategies to reduce or prevent SARS-CoV-2 transmission, including expanded screening testing for asymptomatic persons.[3] Because estimates suggest that over 50% of transmission occurs from persons who are presymptomatic or asymptomatic,[9] expanded screening testing, potentially in serial fashion for reducing transmission in specific venues (e.g., institutions of higher education, schools, and congregate housing settings), is essential to interrupting transmission.[3]

Rapid antigen tests can be an important tool for screening because of their quick turnaround time, lower requirement for resources, high specificity, and high PPV in settings of high pretest probability (e.g., providing testing to symptomatic persons, to persons with a known COVID-19 exposure, or where community transmission is high). Importantly, the faster time from testing to results reporting can speed isolation of infectious persons and will be particularly important in communities with high levels of transmission.

Although the sensitivity of the BinaxNOW antigen test to detect infection was lower compared with real-time RT-PCR, it was relatively high among specimens with positive viral culture, which might reflect better performance for detecting infection in a person with infectious virus present. Community testing strategies focused on preventing transmission using antigen testing should consider serial testing (e.g., in kindergarten through grade 12 schools, institutions of higher education, or congregate housing settings), which might improve test sensitivity in start highlightdetectingend highlight infection.[10] When the pretest probability for receiving positive SARS-CoV-2 test results is elevated (e.g. for symptomatic persons or for persons with a known COVID-19 exposure) a negative antigen test result should be confirmed by NAAT. Asymptomatic persons who receive a positive BinaxNOW antigen test result in a setting with a high risk for adverse consequences resulting from false-positive results (e.g. in long-term care facilities) should also receive confirmatory testing by NAAT.[1]

Despite their reduced sensitivity to detect infection compared with real-time RT-PCR, antigen tests might be particularly useful when real-time RT-PCR tests are not readily available or have prolonged turnaround times. Persons who know their positive test result within 15–30 minutes can isolate sooner, and contact tracing can be initiated sooner and be more effective than if a test result is returned days later. Serial antigen testing can improve detection, but consideration should be given to the logistical and personnel resources needed. All persons receiving negative test results (NAAT or antigen) should be counseled that wearing a mask, avoiding close contact with persons outside their household, and washing hands frequently remain critical to preventing the spread of COVID-19.§§

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