Lung ultrasound combined with C-reactive protein for identifying a bacterial component in children hospitalized with acute lower respiratory tract infections: a prospective observational study

Abstract Acute lower respiratory tract infections (ALRTIs) remain a major cause of pediatric morbidity and antibiotic use. Early identification of a bacterial component is crucial for rational treatment decisions. We evaluated the diagnostic performance of lung ultrasound (LUS), alone and combined with C-reactive protein (CRP), for identifying a clinically adjudicated bacterial component in children hospitalized with ALRTIs. In this prospective study, 160 children (1 month–19 years) hospitalized with ALRTIs underwent LUS within 24 h of admission. LUS-based presumptive classification (viral, bacterial, combined) was assigned using predefined criteria. Final etiological classification was determined independently by three senior pediatricians blinded to LUS findings, using an adjudicated composite reference standard integrating clinical course, laboratory markers, microbiology, and chest radiography. No prespecified biomarker thresholds were applied. Diagnostic performance for identifying a bacterial component (bacterial or combined vs. viral) was assessed using ROC analysis. Seventy-five children (47%) were classified as viral, 60 (37%) as combined, and 25 (16%) as bacterial/atypical according to the adjudicated composite reference standard. Large consolidations (≥ 20 mm), bronchograms, confluent B-lines, and pleural effusions were associated with a bacterial component, whereas viral cases showed small bilateral subpleural consolidations and non-confluent B-lines. LUS demonstrated good diagnostic accuracy (AUROC 0.89, 95% CI 0.84–0.94; sensitivity 83.5%; specificity 94.6%). CRP ≥ 40 mg/L showed comparable performance (AUROC 0.91, 95% CI 0.87–0.96; sensitivity 75.3%; specificity 94.7%). Conclusion : In children hospitalized with ALRTIs, LUS—particularly alongside CRP—may support early bedside identification of a clinically adjudicated bacterial component and assist treatment decisions. What is Known :• Clinical exams and chest X-rays (CXR) poorly distinguish bacterial and combined from viral ALRTIs .• Lung ultrasound (LUS) is validated for diagnosing pneumonia, but its role in identifying the etiology is less studied . What is New :• LUS may help identify the presence of a bacterial component in children hospitalized with ALRTIs .• CRP was the laboratory marker most strongly associated with bacterial component, and its combination with LUS may support early bedside etiological assessment and more rational antibiotic decision-making .