Diagnosis of Respiratory Infections Using Syndromic Panels: A Ct-Based Approach Beyond Qualitative Detection

This retrospective study, conducted between September 2023 and October 2025, evaluated age-related pathogen prevalence, seasonal dynamics, and cycle threshold (Ct) values in nasopharyngeal specimens from hospitalized subjects with suspected acute respiratory infections (ARIs) using the multiplex syndromic panel. A median-based Delta Ct was calculated to define pathogen dominance in co-detections. A total of 2479 nasopharyngeal swabs were analyzed and 54.4% tested positive for at least one pathogen. Overall, the positivity rate and co-detections were found to be significantly higher in pediatric group than in the adult one (p < 0.0001 and p < 0.0001, respectively). Semi-quantitative analysis revealed that RSV and flu viruses maintained low Ct values irrespective of co-detection, whereas RV/EV, Adv, and human bocavirus (HBoV) exhibited significantly higher Ct values when co-detected. RV/EV showed higher Ct values versus human metapneumovirus A/B (p = 0.0014), human parainfluenza virus (p = 0.0007), flu virus (p = 0.0084) and RSV (p < 0.0001). Likewise, Adv demonstrated higher Ct values in comparison to RSV (p = 0.0046). Seasonal drivers typically dominate over persistent agents. Integrating semi-quantitative interpretation into syndromic panel reporting could enhance diagnostic stewardship, optimize antimicrobial use, and improve resource allocation in high-pressure clinical settings.