B73-11 A Rare Case of Disseminated Nocardiosis Presenting With Acute Respiratory Distress Syndrome

Abstract Introduction Nocardia species are partially acid-fast, gram-positive bacilli characterized by their branching filamentous morphology. They are opportunistic pathogens that commonly infect the lungs, central nervous system, or skin. Here, we report a rare case of acute respiratory failure resulting from disseminated Nocardia otitidiscaviarum infection in an immunocompetent patient. Case Presentation An 80-year-old man with a history of bronchiectasis and previously treated pulmonary tuberculosis presented with fever and shortness of breath for one day. He had no history of smoking, recent travel, or contact with sick individuals. Upon arrival at the emergency department, his oxygen saturation was 88% despite receiving oxygen via the non-rebreather mask at 15 L/min. Arterial blood gas analysis revealed pH of 7.29, pCO2 of 50.7 mmHg, pO2 of 69.1 mmHg, and HCO3− of 34.5 mmol/L. Laboratory data showed white blood cell count of 33,020/µL, hemoglobin of 13.5 g/dL, platelet count of 261,000/µL, and C-reactive protein of 34.9 mg/dL. Chest CT demonstrated multiple bilateral pulmonary nodules, bronchiolar wall thickening, and consolidations in the basal lungs. The patient was intubated for acute hypoxemic respiratory failure and subsequently admitted to the ICU for intensive care management. Metagenomic next-generation sequencing (mNGS) of the bronchoalveolar lavage (BAL) sample identified Nocardia otitidiscaviarum. The urine culture collected on the day of admission also yielded gram-positive bacilli, later confirmed as Nocardia otitidiscaviarum. Comprehensive pathogen testing returned negative results for Aspergillus species PCR, cryptococcal antigen, Mycoplasma pneumoniae IgM, Chlamydophila pneumoniae IgM, and cytomegalovirus PCR from blood. Additionally, the FilmArray Pneumonia Multiplex PCR panel, Pneumocystis jirovecii PCR from endotracheal aspirate, COVID-19 and influenza antigen tests from nasal swabs, and urinary Legionella antigen were all negative. To assess potential immunocompromise, an anti-HIV antibody test was performed and was negative. Serum immunoglobulin levels were: IgG 1348 mg/dL, IgA 286 mg/dL, and IgM 37 mg/dL. Following confirmation of nocardiosis, the patient was treated with a combination of meropenem, linezolid, and trimethoprim-sulfamethoxazole. Discussion Disseminated nocardiosis is rare but carries a high fatality rate, with reported mortality reaching approximately 40%. Clinical manifestations are typically non-specific and may include fever, cough, and headache. Unlike the chronic course of localized disease, the disseminated form often progresses rapidly, developing within one week. Although culture remains the diagnostic gold standard, mNGS offers faster and highly sensitive detection in both BAL and blood samples. The prompt use of these diagnostic tools enables early recognition of uncommon infections and facilitates targeted antimicrobial therapy. This abstract is funded by: None