Clinical performance and virological characteristics of the Quick Chaser SARS-CoV-2 rapid antigen assay in symptomatic children

To prospectively evaluate the diagnostic performance of the Quick Chaser SARS-CoV-2 rapid antigen assay in symptomatic children using reverse transcription polymerase chain reaction (RT-PCR) as the reference standard and identify factors associated with discordant antigen results. We conducted a prospective observational study of symptomatic children who underwent paired antigen testing and RT-PCR using the same nasopharyngeal specimen between September and December 2022. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall agreement were assessed. Cycle threshold (Ct) values, SARS-CoV-2 RNA viral loads, symptom duration, and clinical characteristics were compared between RT-PCR-positive children with positive and negative antigen results. Among 229 children, 63 (27.5%) were RT-PCR positive. The assay demonstrated a sensitivity of 87.3% (95% confidence interval [CI], 76.5–94.4%), specificity of 99.4% (95% CI, 96.7–100.0%), PPV of 98.2% (95% CI, 90.4–100.0%), NPV of 95.4% (95% CI, 91.1–97.8%), and overall agreement of 96.1% (95% CI, 92.7–98.2%). False-negative antigen results were associated with higher Ct values, lower viral loads, and testing on the day of symptom onset. Antigen positivity declined with increasing Ct values and decreasing viral loads and was significantly lower on the day of symptom onset than on Days 1–2. The Quick Chaser SARS-CoV-2 assay demonstrated high diagnostic accuracy in symptomatic children. False-negative results were more frequent in specimens with low viral burden and when testing was performed on the day of symptom onset. These findings may improve interpretation of negative antigen results in pediatric practice.