542 - Age-Dependent Shifts in C-Reactive Protein and Disease Phenotype Across Viral Lower Respiratory Tract Infections in Children: A Multiyear Cohort Study

Publication Number: 1521.542

Jacob Z. Hesen, Hurley Medical Center, Undergraduate student, University of Michigan, Flint, MI, United States

Background: Inflammatory C-reactive protein (CRP) is commonly measured in children with viral lower respiratory tract infection (LRTI), yet its interpretation across ages and pathogens remains uncertain.

Objective: To determine age-dependent and viral pathogen-specific patterns of CRP and their relationship with pneumonia and respiratory severity.

Design/Methods: Retrospective (using ICD-10 codes) cohort study of children ≤ 18 years evaluated in the emergency department for rhinorrhea, cough, respiratory distress and/or apnea (January 2019 - December 2024). Viral pathogens were confirmed using Multiplex PCR testing and CRP was measured on venous blood samples using immunoassay. Patients were categorized into the following age groups: infant 0-12 months, toddler 13-36 months, preschool 37-60 months, school-age ≥ 61 months.
Main Outcomes and Measures:
First serum CRP (mg/L), most common pathogens, rates of pneumonia, respiratory failure, and severe disease (oxygen therapy, high-flow nasal cannula [HFNC], CPAP/BPAP, invasive mechanical ventilation, or pediatric intensive care unit [PICU] admission). Nonparametric tests (Kruskal-Wallis, Mann-Whitney U, χ²) assessed group differences. Acute respiratory failure was defined as low PaO2 or SpO2 and/or hypercarbia. This study was IRB approved with waiver for a consent.

Results: 11,670 cases had 2882 CPR measurements. The median age was 14 months [IQR;7-30] and the most common pathogens were: Rhinovirus/Enterovirus [RV/EV] (944, 32%), Respiratory syncytial virus (RSV), Adenovirus and parainfluenza virus. Median CRP for RV/EV rose from 6.1 mg/L (infants) → 9.9 mg/L (toddlers) → 15.6 mg/L (preschool) → 21.9 mg/L (school-age; p < .001, Figure 1) as pneumonia prevalence doubled (16.5% → 34.1%), while severe disease remained ≈ 53-56% and acute respiratory failure remained around 41-45% (Figure 2). RSV showed low CRP (10.8 mg/L) but greatest severity (67% PICU admission). Adenovirus produced higher CRP (17 mg/L) with lower severity (35%) [Figure 3]. Across viruses, CRP correlated with pneumonia (r ≈ 0.45, p < .01) but not with respiratory support level (no Figures.

Conclusion(s): CRP increases with age and parenchymal involvement but does not predict pathogen severity in viral LRTI. Age- and pathogen-specific interpretation may improve antibiotic stewardship and prognostication

Figure 3. Viral Comparison Heatmap: CRP and Clinical Severity Metrics."
Severity increases from green to orange to red.

Figure 1. CRP (mg/L) by age group among RV/EV-positive children, showing monotonic increase with age (p < .001).
the dashed red line represents trend

Figure 2. Demonstrates that severe disease did not monotonously increase across the age groups