A Case of Legionella Pneumonia Suspected as Typical Pneumonia After Lung Cancer Surgery, Diagnosed by a Repeat Urinary Legionella Antigen Test
Abstract
Legionella pneumophila is a leading cause of severe atypical pneumonia and is associated with high mortality when initial treatment is inadequate. The urinary Legionella antigen test serves as a rapid, first-line diagnostic tool; however, early results may be negative, and antigen shedding can be intermittent. In these situations, timely retesting is essential, especially in postoperative or high-risk patients. We report the case of a 74-year-old man, a former smoker with diabetes and moderate aortic stenosis, who underwent thoracoscopic left lower lobectomy and was discharged on postoperative day (POD) six. He developed a fever on POD 27, accompanied by right upper lobe pneumonia. Outpatient urinary antigen tests for pneumococcus and Legionella were negative, and oral garenoxacin was initiated. However, hypoxemia and inflammation worsened, resulting in urgent admission on POD 30. Broad-spectrum β-lactams (sulbactam/ampicillin, followed by piperacillin/tazobactam) were ineffective. Chest CT revealed enlarging infiltrates and a parapneumonic effusion requiring drainage, despite negative pleural fluid cultures. Given the persistent deterioration of the patient's condition, levofloxacin was added, and the urinary Legionella antigen test (R70829, MIZUHO MEDY Co., Ltd., Tosu, Japan) was repeated on hospital day five (POD 35), which returned positive, confirming Legionella pneumonia. Subsequent targeted therapy with azithromycin (days 6-8 and 13-15), alongside levofloxacin,…
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