A Large Community-Acquired Lung Abscess Caused by Pseudomonas aeruginosa: Diagnostic and Therapeutic Challenges

In immunocompetent hosts without healthcare exposure, Pseudomonas aeruginosa is an uncommon pathogen causing community-acquired lung abscesses. These infections are usually polymicrobial and include oropharyngeal flora. We describe a case of a 52-year-old man who had previously been in good health but presented with a four-day history of anorexia, malaise, and fever. Fever (38.0°C), tachycardia (107 bpm), and decreased breath sounds with dullness to percussion over the left lower lung region were noted on physical examination. Significant leukocytosis (11.3 × 10³/μL) and elevated C-reactive protein (252.8 mg/L) were found on laboratory investigations. A sizable (9.3 × 9.6 cm) cavitary lesion with peripheral enhancement in the left lower lobe was confirmed by chest radiography and contrast-enhanced computed tomography, consistent with a primary lung abscess. Pseudomonas aeruginosa was identified as the causative pathogen by bronchoscopy and bronchoalveolar lavage, whereas tuberculosis was ruled out by polymerase chain reaction and negative smears. Clinical improvement occurred within 72 hours of initiating targeted intravenous piperacillin-tazobactam 4.5 g every six hours after infectious disease consultation. Without the need for percutaneous drainage, the patient completed a six-week course of antibiotics, including a 14-day intravenous course followed by four weeks of oral ciprofloxacin 750 mg twice daily. This case emphasizes three key lessons: (1) the value of multidisciplinary management in balancing prolonged medical therapy and interventional drainage for large abscesses; (2) the critical role of bronchoscopic sampling in identifying atypical pathogens and guiding targeted antimicrobial therapy; and (3) the importance of maintaining diagnostic suspicion for lung abscess in patients with constitutional symptoms even in the absence of classic respiratory complaints.