C48-22 Abrupt ARDS With Tension Pneumothorax in an HIV-positive Patient Due to Necrotizing MRSA Pneumonia

Introduction Acute respiratory failure in patients with HIV requires broad consideration of infectious and noninfectious causes. While Pneumocystis jirovecii pneumonia (PJP) is often prioritized, bacterial etiologies like necrotizing methicillin-resistant Staphylococcus aureus (MRSA) pneumonia can evolve rapidly into severe acute respiratory distress syndrome (ARDS) with life-threatening complications. This case highlights the diagnostic complexity and dynamic clinical course of necrotizing MRSA pneumonia in an immunocompromised host, ending in recurrent ARDS and tension pneumothorax. Case Presentation A 40-year-old unhoused man with HIV (CD4 205 cells/µL, undetectable viral load), asthma, bipolar disorder, and polysubstance use was found minimally responsive after suspected opioid overdose. He was naloxone-responsive and required supplemental oxygen. Initial evaluation showed acute kidney injury, rhabdomyolysis, and right lower lobe infiltrates. Broad-spectrum antibiotics and IV fluids were started.By hospital day 3, he developed acute hypoxic and hypercapnic respiratory failure with early ARDS (PaO2/FiO2 <200), prompting intubation. Given the HIV status and aspiration risk, therapy was broadened to include vancomycin, azithromycin, and high-dose trimethoprim-sulfamethoxazole. However, he quickly progressed to septic shock requiring two vasopressors.Bronchoscopy revealed no purulence; BAL was negative for PJP and Mycobacterium Tuberculosis. Nonetheless, cultures later confirmed MRSA. Despite ventilator optimization, worsening oxygenation necessitated prone positioning for severe ARDS (P/F <100), with transient improvement.He was extubated on hospital day 8 but rapidly decompensated with hypoxia and hypotension. Examination revealed absent breath sounds on the right, and chest radiograph confirmed a tension pneumothorax with mediastinal shift. Two emergent pigtail catheters were placed, but persistent hypoxemia required re-intubation. Chest CT demonstrated progressive necrotizing pneumonia with cavitation. Prone ventilation was resumed, MRSA-directed therapy with vancomycin and Ceftaroline continued, and although oxygenation improved, he remained vasopressor-dependent in a guarded condition. Discussion This case demonstrates the volatile trajectory of necrotizing MRSA pneumonia in an immunocompromised patient, including recurrent ARDS and barotrauma. While initial concern included aspiration and PJP, prompt culture data shifted management toward a focused bacterial etiology. The post-extubation deterioration likely reflected both ongoing parenchymal destruction and dynamic air leak physiology from weakened lung architecture. The development of tension pneumothorax highlights the susceptibility of necrotic lung tissue to rupture under positive-pressure ventilation. This case highlights the necessity of real-time diagnostic reassessment and readiness to escalate support as the clinical course in necrotizing infections can abruptly reverse even after apparent stabilization. This abstract is funded by: na