C-Reactive Protein Is Associated with Severity in Hospitalized Children with Respiratory Syncytial Virus Bronchiolitis

Background: Acute bronchiolitis, primarily caused by respiratory syncytial virus (RSV), is the leading cause of hospitalization in young children. Despite international guidelines supporting clinical diagnosis, laboratory evaluations are often conducted with limited validity. Objectives: To evaluate the association between C-reactive protein (CRP) serum levels on admission and disease severity in children hospitalized due to RSV bronchiolitis. Methods: This retrospective cohort study included children (0-24 months old) who were hospitalized due to RSV bronchiolitis (2018-2022), CRP levels taken at admission. Results: We included 1874 children (mean age of 6.7 months, 59% males); median CRP level 1.92 mg/dl. Children with elevated CRP (> 1.92 mg/dl) were significantly older (5.1 vs. 3.8 months, P< 0.001) and had higher rates of pneumonia (9.4% vs. 4.3%, P< 0.001), urinary tract infection (UTI), (2.2% vs. 0.2%, P < 0.001), acute otitis media (AOM) (1.7% vs. 0.2%, P < 0.001 ), admissions to the pediatric intensive care unit (PICU) (7.4% vs. 3.7%, P < 0.001), antibiotic treatment (49.8% vs. 37.2%, P < 0.001), and longer hospitalizations (3.83 vs. 3.31 days, P < 0.001). Multivariable analysis predicted increased risk for UTI, PICU admission, pneumonia, and longer hospitalization (relative risk 11.6, 2.25, 1.98, 1.44, respectively, P < 0.001). CRP thresholds of 3.51, 1.9, and 2.81 mg/dl for PICU admission, UTI, and pneumonia, were calculated using Youden's index with AUC 0.72, 0.62, and 0.61, respectively. Conclusions: Elevated CRP levels at admission are associated with increased disease severity and higher complication rates in children hospitalized with RSV bronchiolitis.