Field Evaluation of the New Rapid NG-Test® SARS-CoV-2 Ag for Diagnosis of COVID-19 in the Emergency Department of an Academic Referral Hospital

Background: As the COVID-19 pandemic resurges affecting large numbers of patients, rapid, and accurate diagnosis using point-of-care tests is very important. Objectives: To evaluate the NG-Test (R) SARS-CoV-2 Ag (NG-Test) immunoassay for qualitative detection of SARS-CoV-2 antigen in nasopharyngeal (NP) and oropharyngeal (OP) samples compared with RT-PCR, in patients attending the Emergencies of an academic referral hospital. Methods: All adult ambulatory patients presenting to the Emergencies of "Attikon" University hospital (Athens, Greece) within three consecutive hours per day between December 2020 and March 2021 and for whom SARS-CoV-2 PCR testing was requested were included. Two NP and one OP samples obtained from each participant were analyzed to determine the diagnostic performance [sensitivity, specificity, positive/negative predictive values (PPV/NPV)] of the NG-Test (NP/OP swabs) in comparison to the reference RT-PCR (NP swab). Results: Overall, 134/263 (51%) patients tested were RT-PCR positive, whereof 108 (overall sensitivity 81%, 95% CI 73-87%) were NP NG-Test positive (PPV 99%, NPV 83%) and 68 (overall sensitivity 51%, 95% CI 42-59%) were OP NG-Test positive (PPV 100%, NPV 66%). The test's specificity (95% CI) was 99% (95-100%) and 100% (96-100%) for NP and OP swabs, respectively. The assay's sensitivity (95% CI) for high viral load (Ct <= 25) was 99% (92-100%) and 71% (60-81%) for NP and OP swabs, respectively. Conclusions: NG-Test using NP swabs detected almost all patients with high viral loads, showing satisfactory performance as a point-of-care test for NP samples obtained from patients with acute infection.