A Rare Combination of Legionella ARDS and Pulmonary Embolism: A Case Report

Legionnaires' disease is a severe atypical pneumonia caused by Legionella pneumophila, an aerobic gram-negative bacillus acquired through inhalation of aerosolized contaminated water. Although venous thromboembolism (VTE) has been reported in association with severe infections, its occurrence in Legionella pneumonia remains uncommon and has been hypothesized to be related to infection-driven endothelial injury and systemic inflammatory activation. We report a case of a 38-year-old male with alcohol use disorder and chronic pancreatitis who presented with severe hypoxemic respiratory failure and acute respiratory distress syndrome (ARDS) secondary to severe necrotizing Legionella pneumonia. Imaging demonstrated multifocal pneumonia with cavitary changes and a subsegmental pulmonary embolism in the left lower lobe. The patient met criteria for ARDS based on the 2023 Global Definition of ARDS. He was treated with targeted antibiotic therapy and anticoagulation, later transitioned to oral therapy, and discharged on room air in stable condition. This case highlights the occurrence of pulmonary embolism in the setting of severe Legionella pneumonia and ARDS. While chronic pancreatitis and critical illness are recognized prothrombotic conditions, infection-related hyperinflammation and endothelial dysfunction may have further contributed to thrombotic risk. Clinicians should maintain a high index of suspicion for pulmonary embolism in patients with severe Legionella pneumonia who develop unexplained or disproportionate hypoxemia.