What is the true place of the SARS-CoV-2 rapid point-of-care antigen test in the hospital setting? Lessons learned from real life.

To assist in the clinical management of patients and to support infection control, we tested the use of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) point-of-care antigen test (AgPOC) for unplanned hospitalization, coupled with a nucleic acid amplification test (NAAT) using specimens collected at the same time upon arrival. The aim of this study was to assess the performance of the AgPOC in this specific use compared to NAAT for SARS-CoV-2 diagnosis, in the context of the low prevalence of infection. For 5 months (between two peaks in France of the SARS-CoV-2 pandemic), all patients admitted who undertook the AgPOC/NAAT paired tests were included in the study. AgPOC performances were determined considering the clinical status and the delay of symptoms onset. NAAT and AgPOC results were available for 4425 subjects. AgPOC results showed a homogeneous specificity (>97%) but a low sensitivity at 45.8%. Considering the national guidelines, sensitivity dropped to 32.5% in cases of symptomatic patients with symptoms older than 5 days or more. This study shows the poor performance of AgPOC for entry screening of patients in hospitals. AgPOC may represent a useful tool in the hospital setting only if the use is restricted to patients with consistent symptoms less than 4 days old.

Evaluation of an antigen-based test for hospital point-of-care diagnosis of SARS-CoV-2 infection.

BACKGROUND: An accurate diagnosis is essential to identify and manage SARS-CoV-2 infected patients and implement infection control measures. Although real-time reverse transcription polymerase chain reaction (RT-PCR) is the current recommended laboratory method, several rapid antigen point-of-care tests (POCTs) were developed as frontline testing for SARS-CoV-2 infection diagnosis. OBJECTIVES: The aim of this study was to assess a recently CE-approved POCT, SARS-CoV-2 Ag Test on the LumiraDx™ Platform (LumiraDx GmbH, Cologne, Germany) for the identification of SARS-COV-2 infected subjects at hospital setting. METHODS: LumiraDx POCT was implemented in three hospital settings: adult and pediatric emergency departments and occupational medicine department along two-month period during the second peak of Italian SARS-CoV-2 pandemic. Rapid antigen testing was performed on direct nasal swabs and results were compared with those obtained by Xpert Xpress SARS-CoV-2 assay. RESULTS: Overall sensitivity, specificity, NPV and PPV were 90.3%, 92.1%, 95.1%, and 84.9%, respectively, compared to reference method. Sensitivity, specificity, PPV and NPV for symptomatic group were 89.3% [95% IC 84.2-93.3], 88.2% [95% IC 72.5-96.7], 97.8% [95% IC 94.6-99.1], and 58.8% [95% IC 48.4-68.5], respectively. Sensitivity, specificity, PPV and NPV for asymptomatic group were 92.1% [95% IC 85-96.5], 92.3% [95% IC 89.9-94.4], 67.9% [95% IC 61.3-73.8], and 98.5% [95% IC 97.1-99.2], respectively. False positive and negative antigen testing results in both symptomatic and asymptomatic group were observed. CONCLUSION: SARS-CoV-2 Ag POCT may represent an interesting tool to rapidly identify symptomatic or asymptomatic infected subjects. However, in hospital setting in which false negative or false positive results may have relevant implications, confirmatory NAAT always remains necessary for the appropriate management of patients.