Diagnostic performance of antigen-based rapid test kits for six respiratory viruses in children: comparison with a multiplex PCR panel and correlation with viral load

ABSTRACT Rapid antigen tests are widely used for point-of-care diagnosis of respiratory tract infection (RTI) in children, but how the sensitivity is influenced by viral load has not been comprehensively characterized across multiple pediatric respiratory viruses. In this prospective, paired-specimen study conducted at the pediatric center, two simultaneous nasopharyngeal swabs were obtained from children with RTI. One swab was tested using antigen-based rapid test kits (ImunoAce series, Tauns Laboratories, Inc.) for SARS-CoV-2, influenza A, influenza B, adenovirus, human metapneumovirus (hMPV), and respiratory syncytial virus; the other was tested using the FilmArray Respiratory Panel (bioMérieux). Specimens positive by either method underwent confirmatory quantitative real-time PCR to determine viral load. Sensitivity was stratified by viral load. A total of 1,584 paired specimens from 1,232 children (median age: 3.0 years [IQR: 1.0–6.0]; 53.7% male) were analyzed. Sensitivity of the antigen tests ranged from 20.6% (adenovirus) to 79.7% (hMPV), while specificity exceeded 99% for all six targets and overall agreement ranged from 90.7% to 99.0%. For every virus, antigen test positivity increased steeply with viral load, approaching 90–100% at viral loads ≥10 6 –10 7 copies/100 µL and falling below 50% at loads ≤10 4 –10 5 copies/100 µL. Antigen-based rapid tests for common pediatric respiratory viruses showed high specificity and viral-load-dependent sensitivity, detecting nearly all specimens with high viral load regardless of the target virus. These findings support a role for antigen testing in identifying children with the highest viral burden—who are most likely to have acute infection. IMPORTANCE The sensitivity of rapid antigen tests for respiratory viruses relative to PCR-based testing has been incompletely characterized. This study evaluated antigen tests for six common pediatric respiratory viruses—SARS-CoV-2, influenza A, influenza B, adenovirus, human metapneumovirus, and respiratory syncytial virus—against a multiplex PCR reference standard across 1,584 clinical specimens and linked test performance directly to quantitative viral load. We show that antigen test sensitivity is strongly and consistently dependent on viral load, approaching 90–100% at high viral loads with very high specificity across all six targets. These findings clarify the clinical role of rapid antigen testing: it reliably identifies children with the highest viral burden, who are most likely to have acute, symptomatic infection warranting immediate clinical action.