Feasibility and Effectiveness Assessment of SARS-CoV-2 Antigenic Tests in Mass Screening of a Pediatric Population and Correlation with the Kinetics of Viral Loads

Abstract

The gold standard for diagnosis of SARS-CoV-2 infection has been nucleic acid amplification tests (NAAT). However, rapid antigen detection kits (Ag-RDTs), may offer advantages over NAAT in mass screening, generating results in minutes, both as laboratory-based test or point-of-care (POC) use for clinicians, at a lower cost. We assessed two different POC Ag-RDTs in mass screening versus NAAT for SARS-CoV-2 in a cohort of pediatric patients admitted to the Pediatric Emergency Unit of IRCCS—Polyclinic of Sant’Orsola, Bologna (from November 2020 to April 2021). All patients were screened with nasopharyngeal swabs for the detection of SARS-CoV-2-RNA and for antigen tests. Results were obtained from 1146 patients. The COVID-19 Ag FIA kit showed a baseline sensitivity of 53.8% (CI 35.4–71.4%), baseline specificity 99.7% (CI 98.4–100%) and overall accuracy of 80% (95% CI 0.68–0.91); the AFIAS COVID-19 Ag kit, baseline sensitivity of 86.4% (CI 75.0–93.9%), baseline specificity 98.3% (CI 97.1–99.1%) and overall accuracy of 95.3% (95% CI 0.92–0.99). In both tests, some samples showed very low viral load and negative Ag-RDT. This disagreement may reflect the positive inability of Ag-RDTs of detecting antigen in late phase of infection. Among all cases with positive molecular test and negative antigen test, none showed viral loads > 106 copies/mL. Finally, we found one false Ag-RDTs negative result (low cycle thresholds; 9 × 105 copies/mL). Our results suggest that both Ag-RDTs showed good performances in detection of high viral load samples, making it a feasible and effective tool for mass screening in actively infected children.

Diagnostic accuracy of a SARS-CoV-2 rapid antigen test among military and civilian personnel of an Air Force airport in central Italy

“…Other studies have previously assessed the diagnostic accuracy of AFIAS [ 10 , 11 , 14 ]. A Korean study performed on clinical specimens from 38 adult COVID-19 and 122 non-COVID-19 patients showed an excellent SP (0.987–0.989), but the sensitivity was good only for NPSs with high viral load (0.913–1.00 in NPSs with Ct <25) [ 10 ].…”

“…Another study assessed the accuracy of AFIAS COVID-19 Ag in a mass screening carried out among unselected paediatric patients. Overall sensitivity and specificty were 86.4% and 98.3%, respectively [ 11 ]. Also in that study, information about distribution of Ct values as well as presence of symptoms were not reported, precluding any detailed comparison with results of the present study.…”

“…Since December 2020, the EU case definition for COVID-19 includes the detection of antigens in the clinical specimens and therefore the use of RADTs as a diagnostic method [19,20]. Currently available RADTs show a variable but lower sensitivity compared to RT-PCR test, while their specificity is generally high [6][7][8][9][10][11][12][13][14][15][16][17]. It is worthy of note that RADTs are sensitive enough to detect cases with a high viral load [i.e.…”

“…RADTS have proved particularly suitable as point of care tests (POCT), since they are economical, not requiring the use of particularly complex instrumentation, and have shorter turnaround time (less than 30 minutes). RADTs are primarily lateral flow immunochromatographic assays that detect viral antigen in NPSs by means of a device coated with anti-SARS-CoV-2 antibody [6][7][8][9][10][11][12][13][14][15][16][17].…”

“…According to a recent systematic review, the average sensitivity and specificity of RADTs were 0.562 and 0.995, respectively [13]. In general, RADTs perform well in NPSs with high viral load or with low cycle threshold (Ct) in RT-PCR for SARS-CoV-2 tests [6][7][8][9][10][11][12][13][14][15][16][17]. The Ct refers to the number of cycles needed to amplify a fragment of viral genome to reach a threshold level.…”