Effectiveness of Abbott BinaxNOW Rapid Antigen Test for Detection of SARS-CoV-2 Infections in Outbreak among Horse Racetrack Workers, California, USA

Krishna Surasi; Kristin J. Cummings; Carl Hanson; Mary Kate Morris; Maria Salas; David Seftel; Liza Ortiz; Ruwan Thilakaratne; Cameron Stainken; Debra A. Wadford

Disclosures

Emerging Infectious Diseases. 2021;27(11):2761-2767. 

In This Article

Abstract and Introduction

Abstract

The Abbott BinaxNOW rapid antigen test is cheaper and faster than real-time reverse transcription PCR (rRT-PCR) for detecting severe acute respiratory syndrome coronavirus 2. We compared BinaxNOW with rRT-PCR in 769 paired specimens from 342 persons during a coronavirus disease outbreak among horse racetrack workers in California, USA. We found positive percent agreement was 43.3% (95% CI 34.6%–52.4%), negative percent agreement 100% (95% CI 99.4%–100%), positive predictive value 100% (95% CI 93.5%–100%), and negative predictive value 89.9% (95% CI 87.5%–92.0%). Among 127 rRT-PCR–positive specimens, the 55 with paired BinaxNOW-positive results had a lower mean cycle threshold than the 72 with paired BinaxNOW-negative results (17.8 vs. 28.5; p<0.001). Of 100 specimens with cycle threshold <30, a total of 51 resulted in positive virus isolation; 45 (88.2%) of those were BinaxNOW-positive. Our comparison supports immediate isolation for BinaxNOW-positive persons and confirmatory testing for negative persons.

Introduction

Rapid antigen tests, such as Abbott BinaxNOW (https://www.abbott.com) test kits, offer a less expensive and faster alternative to nucleic acid amplification tests, such as real-time reverse transcription PCR (rRT-PCR), in the diagnosis of coronavirus disease (COVID-19).[1,2] Previous studies of BinaxNOW compared with rRT-PCR have demonstrated a high negative percent agreement (NPA) (99.4%–100%) but variable positive percent agreement (PPA) (52.5%–89.0%). Performance was better among symptomatic persons, specimens with cycle threshold (Ct) <30 (suggestive of higher viral loads), and specimens with positive viral cultures.[3–8] These reports have focused on community testing sites and outbreaks in healthcare facilities.

Throughout the pandemic, certain nonhealthcare occupational groups (e.g., meat and poultry processing workers) have experienced higher risk of contracting COVID-19; this higher risk is attributable to workplace hazards, such as lack of appropriate personal protective equipment, densely populated work areas, poorly ventilated workspaces, and prolonged close contact.[9,10] These workplaces might benefit from effective rapid antigen tests that enable employers to quickly identify persons infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for isolation and to guide contact tracing, thereby reducing workplace transmission. Despite the need for research on this topic, information on the performance of BinaxNOW in the setting of nonhealthcare workplace outbreaks is lacking.

During October 20, 2020–January 15, 2021, a horse racetrack (the facility) in California, USA, experienced a COVID-19 outbreak among its 563 employees and independent contractor workers (hereafter collectively called facility staff). Nearly half (n = 278; 49.4%) of the staff lived onsite in facility-provided housing, and many performed essential duties (e.g., grooming, feeding) related to the basic care of the >1,100 horses stabled there.

The outbreak was discovered by the contact tracing efforts of the local health department (LHD), the City of Berkeley Public Health Officer Unit. In response, the LHD ordered that all nonessential work activities (e.g., horse racing) be stopped until mass testing of all staff demonstrated no further transmission. The initial round of rRT-PCR testing (round 0) occurred on November 14–15, 2020, and identified 169 SARS-CoV-2–positive staff who were subsequently isolated. At this time, all staff were assumed to have been exposed. Those living onsite were moved to hotel rooms to quarantine, and those living offsite quarantined in their homes. No staff were permitted to return to onsite residence until the outbreak had ended. However, some quarantined employees were permitted to return to work if they were needed to perform duties related to essential care of the horses. Additional rounds of testing were needed to monitor ongoing transmission and determine when the outbreak had ended. The LHD decided to use BinaxNOW as a supplement to rRT-PCR to more quickly identify SARS-CoV-2–positive employees for isolation. This use provided an opportunity to assess the effectiveness of the BinaxNOW rapid antigen test in detecting SARS-CoV-2 infection in a nonhealthcare workplace outbreak. The purpose of this analysis is to compare BinaxNOW with rRT-PCR in paired specimens from persons during a COVID-19 outbreak among horse racetrack workers. These findings could inform testing protocols used to contain future outbreaks of COVID-19 in nonhealthcare workplaces.

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