SARS-CoV-2 Antigen Detection to Expand Testing Capacity for COVID-19: Results from a Hospital Emergency Department Testing Site
Giulia Menchinelli, Giulia De Angelis, Margherita Cacaci, Flora Marzia Liotti, Marcello Candelli, Ivana Palucci, Rosaria Santangelo, Maurizio Sanguinetti, Giuseppe Vetrugno, Francesco Franceschi, Brunella Posteraro
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.