Snapshot A 65-year-old male presents with a 5 day history of high fever, cough, and diarrhea after returning from a 2 week cruise to the Carribean. Patient has COPD with a 30 pack-year history of cigarette smoking. Temperature is 100.2°F (39°C), respirations are 24/min, BP is 100/60mmHg, pulse is 90/min and oxygen saturation 87% on room air. Chest exam reveals dull percussion notes at the left lung base. Chest radiograph reveals left lobar infiltrate, with patchy opacities on the right. Complete metabolic panel revealed a hyponatremia of 130 mEq/L, serum creatinine of 1.0 (baseline) and elevated AST/ALT. Complete blood count showed a leucocytosis. A urinary antigen test was positive. Sputum culture results are being awaited, although there only neutrophils detected on Gram stain. Introduction Classification bacteria other gram-negative Legionella L. pneumophila Presentation Legionnaires' disease severe atypical pneumonia "fever, cough, diarrhea, especially in a smoker" high fever (>39°C) low heart rate confusion hyponatremia(<130mEq/L) diarrhea although no bacteria seen in GI tract Pontiac fever mild flu-like syndrome Differential Other etiologies of atypical pneumonia Mycoplasma Chlamydia Typical community acquired pneumonia S. pneumoniae Evaluation Labs are essential because clinical presentation is nonspecific, LFTs may be elevated 2 most important tests culture weakly gram-negative stain with silver instead urinary antigen test avoids need for sputum sample remains positive even after empiric antibiotic therapy available in hours vs. 3-5 days for culture specific for serogroup 1 only by far the most common serogroup Also used DFA staining of sputum serology PCR Treatment Erythromycin, azithromycin, levofloxacin Penicillin is not effective Prognosis, Prevention and Complications Prognosis good if treated promptly with antibiotics worse in the immunocompromised Prevention routine cultures of potential water sources(e.g hospitals) monochloramine disinfection of community water supplies decontaminate air conditioners routinely Complications rare, seen more in immunocompromised patients myocarditis, prosthetic valve endocarditis