CT reveals thick-walled cavities (>2 cm diameter) with air-fluid levels and surrounding inflammatory infiltration.Elevated infectious biomarkers (e.g., Procalcitonin/PCT, C-reactive Protein/CRP) and positive microbiological identification of pathogens (e.g., Klebsiella pneumoniae, Pseudomonas aeruginosa) in respiratory samples (sputum/bronchoalveolar lavage fluid) support the diagnosis of bacterial pneumonia while ruling out alternative causes. Here, CRP is linked to bacterial pneumonia.