Performance of a SARS-CoV-2 antigen rapid immunoassay in patients admitted to the emergency department.

ABSTRACT

OBJECTIVES: Given the ongoing pandemic emergency, there is a need to identify SARS CoV-2 infection in various community settings. Rapid antigen testing is spreading worldwide, but diagnostic accuracy is extremely variable. Our study compared a microfluidic rapid antigen test with a reference molecular assay in patients admitted to the emergency department (ED) of a general hospital from October 2020 to January 2021. METHODS: Nasopharyngeal swabs collected in patients with suspected COVID-19 and in patients with no symptoms suggesting COVID-19, but requiring hospitalization, were obtained. RESULTS: 792 patients of median age 71 years were included. With a prevalence of 21%, the results showed 68.7% (95% confidence interval [CI] 60.9-75.5) sensitivity; 95.2% (95% CI 93.1-96.7) specificity; 79.2% (95% CI 71.4-85.3) positive predictive value (PPV); 91.9% (95% CI 89.5-93.9) negative predictive value; 3.8 (95% CI 2.7-5.3) positive likelihood ratio (LR+); and 0.09 (95% CI 0.07-0.1) negative likelihood ratio (LR-). In the symptomatic subgroup, sensitivity increased to 81% (95% CI 70.3-88.6) and PPV to 96.9% (95% CI 88.5-99.5), along with an LR+ of 32 (95% CI 8.2-125.4). CONCLUSIONS: The new rapid antigen test showed an overall excellent diagnostic performance in a challenging situation, such as that of an ED during the COVID-19 emergency.