ABSTRACT
INTRODUCTION: Legionella is an important cause of community acquired pneumonia. Here we describe a case with strong clinical suspicion of Legionella pneumonia despite negative urine antigen but confirmed by polymerase chain reaction (PCR) test on a lower respiratory sample. DESCRIPTION: A 52-year-old male, nonsmoker with unremarkable past medical history presented with a 4-day history of fever, nonproductive cough, and malaise, after returning from a trip to Italy. He underwent Computed Tomography Angiography (CTA) chest which revealed bilateral lung infiltrates at Urgent Care. Both Rapid Ag and PCR test for SARS CoV-2 were negative. He was vaccinated against SARS-CoV2. On hospital admission his oxygen saturation was 85% on room air. Lab work revealed white blood cell (WBC) 22.5, Hemoglobin 12.8, Platelets 397 with 96% neutrophils. His Sodium was 135 mmol/L (135- 146), CRP 433.2 mg/L (normal < 5). Respiratory PCR was negative for Influenza A, B, RSV. Urine Pneumococcal and Legionella Ag were negative. He was started on Ceftriaxone and Azithromycin. He developed rapidly progressing respiratory failure leading to intubation, prone positioning, inhaled Prostacyclin due to significant hypoxia (P/F ratio 57). His antibiotics were changed to high dose Levofloxacin (750 mg IV Q Day) because of strong suspicion of Legionella. He underwent bronchoscopy with BAL and the PCR came back positive for Legionella. The patient was extubated in 48 hours and discharged home after a 10-day course of Levaquin. The BAL sample was sent to Centers for Disease Control and Prevention (CDC) which identified Legionella species as serotype 1. DISCUSSION: Legionella are gram negative facultative intracellular bacteria with soil and water as reservoirs. Legionella grows poorly on routine culture media. Urine antigen (Ag) testing has a sensitivity of 75% and detects Legionella pneumophilia serotype 1, the dominant cause (80% of cases) but does not detect the other 30 Legionella species that have been isolated from humans. A lower respiratory PCR detects other serotypes and perhaps is more sensitive than urine Ag in detecting serotype 1. If clinical suspicion of Legionella is high PCR must be performed on a lower respiratory sample and one must not solely rely on a negative Urinary Ag test.