A Rare and Challenging Polymicrobial Pleural Infection Involving Cupriavidus pauculus in a Patient with Rheumatoid Arthritis and Multiple Complications

A 58-year-old female with a 15-year history of rheumatoid arthritis (RA) and a history of treatment consisting of methotrexate, hydroxychloroquine, leflunomide, and chronic prednisolone therapy, presented with fever, productive cough, dyspnea, and left leg cellulitis. She developed septic shock complicated by tension pneumothorax requiring emergency thoracostomy and non-ST-elevation myocardial infarction (NSTEMI). Pleural fluid culture grew Cupriavidus pauculus, a rare environmental gram-negative bacillus, alongside Burkholderia cepacia and Candida parapsilosis, indicating polymicrobial infection which was most likely predisposed by patient's immunosuppressed state from RA and prolonged steroid use. Treatment consisted of trimethoprim/sulfamethoxazole, meropenem, fluconazole, and cardiopulmonary support, and culminated in recovery after three weeks. This first reported C. pauculus case from Pakistan highlights diagnostic challenges in immunocompromised hosts and underscores the importance of rapid microbiological characterization and multidisciplinary care when managing sepsis caused by rare pathogens amidst complex comorbidities.