• Valeria Cento, Silvia Renica, Elisa Matarazzo, Maria Antonello, Luna Colagrossi, Federica Di Ruscio, Arianna Pani, Diana Fanti, Chiara Vismara, Massimo Puoti, Francesco Scaglione, Carlo Federico Perno, Claudia Alteri, and On Behalf Of The S Co Va Study GroupInfectious Diseases Unit, ASST Grande Ospedale Metropolitano Niguarda, 20162 Milan, Italy..
• Department of Oncology and Hemato-Oncology, Università degli Studi di Milano, 20122 Milan, Italy.
• Viruses Basel. 2021 May 1; 13 (5).

AbstractTo complement RT-qPCR testing for diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, many countries have introduced the use of rapid antigen tests. As they generally display lower real-life performances than expected, their correct positioning as frontline screening is still controversial. Despite the lack of data from daily clinical use, third generation microfluidic assays (such as the LumiraDx SARS-CoV-2 Ag test) have recently been suggested to have similar performances to RT-qPCR and have been proposed as alternative diagnostic tools. By analyzing 960 nasopharyngeal swabs from 960 subjects at the emergency department admissions of a tertiary COVID-19 hospital, LumiraDx assay demonstrated a specificity of 97% (95% CI: 96-98), and a sensitivity of 85% (95% CI: 82-89) in comparison with RT-qPCR, which increases to 91% (95% CI: 86-95) for samples with a cycle threshold ≤ 29. Fifty false-negative LumiraDx-results were confirmed by direct quantification of genomic SARS-CoV-2 RNA through droplet-digital PCR (median (IQR) load = 5880 (1657-41,440) copies/mL). Subgenomic N and E RNAs were detected in 52% (n = 26) and 56% (n = 28) of them, respectively, supporting the presence of active viral replication. Overall, the LumiraDx test complies with the minimum performance requirements of the WHO. Yet, the risk of a misrecognition of patients with active COVID-19 persists, and the need for confirmatory RT-qPCR should not be amended.

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