SARS-CoV-2 Antigen Detection to Expand Testing Capacity for COVID-19: Results from a Hospital Emergency Department Testing Site.

Giulia Menchinelli,Giuseppe Vetrugno,Margherita Cacaci,Flora Marzia Liotti,Francesco Franceschi,Giulia De Angelis,Rosaria Santangelo,Ivana Palucci,Maurizio Sanguinetti,Brunella Posteraro,Marcello Candelli

doi:10.3390/diagnostics11071211

Abstract

Background: SARS-CoV-2 antigen detection has currently expanded the testing capacity for COVID-19, which yet relies on the SARS-CoV-2 RNA RT-PCR amplification. Objectives: To report on a COVID-19 testing algorithm from a tertiary care hospital emergency department (ED) that combines both antigen (performed on the ED) and RT-PCR (performed outside the ED) testing. Methods: Between December 2020 and January 2021, in a priori designated, spatially separated COVID-19 or non-COVID-19 ED areas, respectively, symptomatic or asymptomatic patients received SARS-CoV-2 antigen testing on nasopharyngeal swab samples. Antigen results were promptly accessible to guide subsequent, outside performed confirmatory (RT-PCR) testing. Results: Overall, 1083 (100%) of 1083 samples in the COVID-19 area and 1815 (49.4%) of 3670 samples in the non-COVID-19 area had antigen results that required confirmation by RT-PCR. Antigen positivity rates were 12.4% (134/1083) and 3.7% (66/1815), respectively. Compared to RT-PCR testing results, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of antigen testing were, respectively, 68.0%, 98.3%, 88.8%, and 94.1% in the COVID-19 area, and 41.9%, 97.3%, 27.3%, and 98.6% in non-COVID-19 area. Practically, RT-PCR tests were avoided in 50.6% (1855/3670) of non-COVID-19 area samples (all antigen negative) from patients who, otherwise, would have needed antigen result confirmation. Conclusions: Our algorithm had value to preserve RT-PCR from avoidable usage and, importantly, to save time, which translated into a timely RT-PCR result availability in the COVID-19 area.

Highlights

In the context of a raging pandemic due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), known as the etiological agent of coronavirus disease 2019 (COVID-19), COVID-19 testing strategies are crucial for the timely identification and/or management of persons with SARS-CoV-2 infection [1,2]
Using the above-mentioned sensitivity and specificity values, we explored the relationship between predictive values (PPV and negative predictive value (NPV)) and the probability of testing positive in both COVID-19 and non-COVID-19 areas (Supplementary Table S1)
Taking advantage of current antigen-based testing strategies to cope with COVID19 [19], we identified two areas in the emergency department (ED) that differed with respect to the pre-test probability of patient samples (n = 4753, in total) being tested with the SD Biosensor STANDARD F COVID-19 Ag fluorescent immunoassay (FIA)

Summary

Introduction

In the context of a raging pandemic due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), known as the etiological agent of coronavirus disease 2019 (COVID-19), COVID-19 testing strategies are crucial for the timely identification and/or management of persons with SARS-CoV-2 infection [1,2]. Since Europe has become the epicenter of the pandemic as of March 2020, the emergency department (ED) in many Italian hospitals is struggling with an overwhelming influx of persons who need daily, prompt, and accurate testing for COVID-19 [3] This generates many samples—preferably nasopharyngeal swab samples—that daily reach hospital laboratories for COVID-19 diagnosis, which mostly relies on the amplification of SARS-CoV-2 RNA using reverse-transcription polymerase chain reaction (RT-PCR) [4]. Despite not being as sensitive as RT-PCR [4], antigen testing can be highly specific, deployed outside the clinical microbiology laboratory, and, importantly, provide a result within 15–30 min [10] This is thanks to a lateral-flow technology that allows SARS-CoV-2 antigen to be detected and visualized as an immunoassay reactive band directly on a small portable device [11]. Conclusions: Our algorithm had value to preserve RT-PCR from avoidable usage and, importantly, to save time, which translated into a timely RT-PCR result availability in the COVID-19 area

Objectives

Methods

Results

Discussion

Conclusion