Comparison of Quidel Sofia SARS FIA test to Hologic Aptima SARS-CoV-2 TMA test for diagnosis of COVID-19 in symptomatic outpatients


Department of Microbiology, ACL Laboratories, Aurora West Bend Clinic, Department of Urgent Care, Primary Care Service Line, Aurora Health Care Medical Group


The Quidel Sofia SARS FIA test (SOFIA) is a rapid antigen immunoassay for detection of SARS-CoV-2 viral proteins from nasal or nasopharyngeal swab specimens. The purpose of this study was to compare the results of the SOFIA test to the Hologic Aptima SARS-CoV-2 TMA test (APTIMA TMA), a high-throughput molecular diagnostic test that uses transcription mediated amplification for detection of SARS-CoV-2 nucleic acid from upper respiratory specimens. Three hundred and 40-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 on the SOFIA test and nasopharyngeal swabs on the APTIMA TMA test. The SOFIA test demonstrated an 82.0% positive percent agreement (PPA) compared to the APTIMA TMA test for symptomatic patients tested ≤ 5 days from symptom onset and a 54.5% PPA for symptomatic patients > 5 days from symptom onset. The Cepheid Xpert Xpress SARS-CoV-2 RT-PCR test was used to determine the cycle threshold (Ct) value from any specimens that were discrepant between the SOFIA and APTIMA TMA tests. Using a Ct 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 that were likely to be culture positive.

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