Discrepant specimens were run in a second molecular test, the Cepheid Xpert Xpress SARS-CoV-2 reverse transcription-PCR (RT-PCR) test (XPERT), to determine the cycle threshold ( C T) value and to better assess the clinical significance of the false-negative SOFIA test results. The accuracy of the test was further stratified by the number of days post–symptom onset and by patient age. This report compares the results of the SOFIA test to those of the APTIMA TMA test for patients presenting to the urgent care department with signs and symptoms of COVID-19. Due to limited data on the accuracy of the SOFIA test and reports of false-positive results ( accessed 27 October 2020), as well as historical data showing lower sensitivity of rapid antigen tests than of molecular tests, this site collected a second specimen, during the same visit, from all patients for confirmatory testing with the Hologic Aptima SARS-CoV-2 transcription-mediated amplification (TMA) test (APTIMA TMA) in the central laboratory of ACL Laboratories ( 1, – 4). During that period, specimens from these patients were sent to a reference lab for molecular testing, with a positivity rate of approximately 18%. In the month prior to the implementation of antigen testing, this site saw approximately 20 patients with signs and symptoms of COVID-19 each day. These data were collected at an urgent care center serving patients in an area with a high prevalence of SARS-CoV-2. Recently, Advocate Aurora Health (and ACL Laboratories, which is owned and operated by Advocate Aurora Health) implemented the SOFIA test in several urgent care centers for the diagnosis of coronavirus disease from 2019 (COVID-19) on patients experiencing signs and symptoms of upper respiratory tract infection. If viral proteins are not present above a specific concentration, then no fluorescence will be detected, and the test will be negative. The fluorescence is measured using either a Quidel Sofia or a Quidel Sofia 2 test device. If the viral proteins are present in the test specimen, a fluorescent band will be present at a specific location on the test strip. The test is a sandwich-style lateral-flow immunoassay that is used to detect the nucleocapsid protein of SARS-CoV-2. Specimens are collected and placed directly into a reaction tube containing a reaction solution. This test is performed using either nasal or nasopharyngeal swabs and can be completed in approximately 15 min. The first of these tests to receive EUA status was the Quidel Sofia SARS Antigen FIA (fluorescent immunoassay) test (SOFIA), on 17 July 2020 ( accessed 27 October 2020). In addition to molecular diagnostic tests, seven rapid antigen tests have received Emergency Use Authorization (EUA) for the diagnosis of SARS-CoV-2 infection. Using a C T value of ≤35 as a surrogate for SARS-CoV-2 culture positivity, we estimate that the SOFIA test detected 87.2% of symptomatic patients tested ≤5 days from symptom onset who were likely to be culture positive.Īt present, diagnosis of active severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection relies primarily on the use of molecular diagnostic testing. The Cepheid Xpert Xpress SARS-CoV-2 reverse transcription-PCR (RT-PCR) test was used to determine the cycle threshold ( C T) value for any specimens that were discrepant between the SOFIA and APTIMA TMA tests. The SOFIA test demonstrated a positive percent agreement (PPA) of 82.0% with the APTIMA TMA test for symptomatic patients tested ≤5 days from symptom onset and a PPA of 54.5% for symptomatic patients >5 days from symptom onset. Three hundred forty-seven symptomatic patients from an urgent care center in an area with a high prevalence of SARS-CoV-2 infections were tested in parallel using nasal swabs for the SOFIA test and nasopharyngeal swabs for the APTIMA TMA test. The purpose of this study was to compare the results of the SOFIA test to those of the Hologic Aptima SARS-CoV-2 TMA test (APTIMA TMA), a high-throughput molecular diagnostic test that uses transcription-mediated amplification (TMA) for the detection of SARS-CoV-2 nucleic acid from upper respiratory tract specimens. The Quidel Sofia severe acute respiratory syndrome (SARS) fluorescent immunoassay (FIA) test (SOFIA) is a rapid antigen immunoassay for the detection of SARS coronavirus 2 (SARS-CoV-2) proteins from nasal or nasopharyngeal swab specimens.
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