Human Metapneumovirus Versus Respiratory Syncytial Virus in the Pediatric Emergency Department: Inflammatory Indices, Cycle-Threshold Profiles and Outcomes.

Inflammatory-biomarker, cycle-threshold (Ct) and co-detection data on human metapneumovirus (hMPV) in the pediatric emergency department remain scarce. We retrospectively studied 203 children with multiplex RT-PCR-confirmed respiratory virus positivity at a tertiary pediatric emergency department (January-May 2025). Inflammatory indices, C-reactive protein (CRP) and per-target Ct were compared between hMPV and RSV; predictors of antibiotic prescribing were assessed by ROC and multivariable regression. hMPV (17.7%) and RSV (28.6%) were dominant detections; co-detection 24.1%. Compared with RSV, hMPV affected older children with higher comorbidity, more pneumonia and neutrophil-driven inflammation (neutrophil-to-lymphocyte ratio [NLR], systemic immune-inflammation index [SII], CRP higher; p ≤ 0.006). Dominant Ct differed across pathogens (Kruskal-Wallis p < 0.001); rhinovirus carried the lowest viral load. Paired non-dominant Ct exceeded dominant Ct (median ΔCt +3.6, p = 0.013). CRP independently predicted antibiotic prescribing (AUC 0.78, cut-off 3.9 mg/L). hMPV showed a neutrophil-dominant inflammatory phenotype in older, more comorbid children than RSV. Per-target Ct supports the lowest-Ct-dominant convention. CRP-not white-cell indices-drove antibiotic prescribing; a 3.9 mg/L cut-off supports stewardship in PCR-confirmed pediatric viral respiratory infection.