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Legionella Pneumonia

Dr. Sinkoff presents the case of a middle aged gentleman who presented with confusion, hyponatremia and pneumonia ultimately diagnosed with legionella.





Teaching points:

1. Pneumonia classifications:

  • Community Acquired pneumonia

  • Health care associated pneumonia: within 90 days of hospitalization, visitation to hemodialysis, residence in long term facility

  • Hospital acquired pneumonia: >/= 48 hours after admission

  • Ventilator associated pneumonia: >/= 48 hours after intubation


2. Legionella makes up 2-15% of all community-acquired pneumonia cases that required hospitalization

  • Inhalation of aerosols containing legionella, microaspiration of contaminated water

  • Infection may occur without obvious source

  • Classically hotels, hospitals, cruise ships, office buildings

  • Can be severe in presentation - complicated by stupor, respiratory failure, multiorgan failure, diarrhea

  • Hyponatremia is a hint that a pneumonia might be legionella

  • Diagnosis is better made by urine antigen test (sensitivity of 68-81%, specificity of 98-99%). Urine antigen testing evaluates for serotype 1 infection, results can remain positive for prolonged periods after initial infection

  • Culture only has a sensitivity of 60-61% and has a >48 hour incubation period.

  • Treat with levofloxacin or azithromycin


3. How do we risk stratify patients with pneumonia?

CURB-65 scoring:




4. What is the best way to rule out a PE in a patient that presents with symptoms of dyspnea, tachycardia, and hypoxia?


PERC criteria: can be applied to a subset of patients at very low risk - these patients don't even require a D-dimer

---> In a recent meta-analysis, if the PERC were applied only 0.3% of PEs would have been missed, and 22% of D-dimer testing would have been avoided

---> If PERC is >0, D0dimer should be pursued



 

Wells Criteria for PE


Low pretest probability + negative D-Dimer: no imaging necessary



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