Respiratory panel detections, inflammatory biomarkers, and length of stay in children hospitalized with acute respiratory tract infections: a retrospective cohort study

Qualitative respiratory-panel detections and inflammatory markers are often considered together in hospitalized children, but neither identifies the cause of illness on its own. We examined associations between panel detections and routinely recorded biomarkers, radiographic findings, and length of stay (LOS). This retrospective study included children aged ≤ 18 years hospitalized with acute respiratory tract infections at Hangzhou Children’s Hospital, China, between 5 January 2023 and 17 June 2025. A 13-target pharyngeal-swab assay was summarized as 11 analytical groups. Primary outcomes were high-sensitivity C-reactive protein (hsCRP) ≥20 mg/L, procalcitonin (PCT) ≥0.5 ng/mL, and LOS ≥ 7 days. Complete-case logistic models adjusted for age group, sex, testing year, and season. Sensitivity analyses assessed continuous biomarkers, multiple-target detections, recorded severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) positivity, and sampling within 24 or 48 hours of admission using source records and chart-reviewed intervals. Among 6093 children, 2076 were panel-negative, 3343 had single-target detection, and 674 had multiple-target detection. Compared with panel-negative children, human adenovirus detection was associated with hsCRP ≥ 20 mg/L (adjusted odds ratio [aOR], 2.19; 95% confidence interval [CI], 1.63–2.96) and PCT ≥ 0.5 ng/mL (aOR, 1.93; 95% CI, 1.34–2.77). Mycoplasma pneumoniae (MP) detection was associated with LOS ≥ 7 days (aOR, 2.57; 95% CI, 1.99–3.31) and lower odds of PCT ≥ 0.5 ng/mL (aOR, 0.22; 95% CI, 0.13–0.37). The MP–LOS aORs were 2.50 (1.82–3.44) and 2.76 (2.12–3.59) in the 24-hour and 48-hour subsets. Multiple-target detection was also associated with LOS ≥ 7 days (aOR, 2.21; 95% CI, 1.73–2.82). Detection groups differed in recorded biomarker and hospitalization measures. Early-sampling restrictions supported the persistence of the MP–LOS association but did not establish causation. Unmeasured bacterial infection, treatment, illness severity, and clinical selection preclude pathogen-causal or prognostic interpretation.