Updated: 12/19/2019

Legionnaires Disease

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Snapshot
  • A 75-year-old woman returns from a week-long cruise with a cough and sputum production. Her family notices that she seems more confused than usual and brings her into the hospital. Earlier today, she had complained of nausea and vomiting. On physical exam, her pulse is 60/min. There are fine crackles diffusely on chest auscultation. Laboratory tests show that she has hyponatremia and mildly elevated transaminitis. A urine antigen test is positive for the suspected disease and she is started on antibiotics.
Introduction
  • Classification
    • Legionella pneumophila
      • an aerobic, facultative, intracellular gram - rod
    • transmission
      • aspiration of contaminated water/soil
        • air conditioning
        • hot tubs
        • swimming pools
  • Epidemiology
    • demographics
      • more common in the elderly
    • risk factors
      • cruise ships
      • smoking
      • immunosuppression
      • hospitalization
  • Pathogenesis
    • organism is phagocytosed into alveolar macrophages, where they replicate
    • bacterial spread occurs when they escape from macrophage vacuoles leading to host cell osmotic lysis
  • Associated conditions
    • Legionnaires disease (most common)
      • lobar or insterstitial pneumonia
      • gastrointestinal and central nervous system involvement
      • more common in smokers and those with chronic lung diseases
Presentation
  • Symptoms
    • cough with sputum production
    • gastrointestinal symptoms
    • nausea or vomiting
    • water diarrhea
    • central nervous system symptoms
      • confusion
      • encephalopathy
  • Physical exam 
    • fever
    • altered mental status
    • dyspnea
    • relative bradycardia
    • pneumonia
Imaging
  • Chest radiography
    • indication
      • all patients
    • findings
      • lobar consolidation or
      • diffuse patchy infiltrates
Studies
  • Labs
    • urine antigen test 
      • diagnostic
    • does not Gram stain well, so this requires a silver stain
    • sputum culture
      • requires special media for culture
      • charcoal yeast extract agar buffered with iron and cysteine 
    • hyponatremia
    • transaminitis
  • Making the diagnosis
    • based on clinical presentation and laboratory studies
Differential
  • Mycoplasma pneumoniae
    • distinguishing factor
      • typically does not present with gastrointestinal or central nervous system involvement
Treatment
  • Medical
    • antibiotics
      • indication
        • all patients
      • drugs
        • macrolides
        • respiratory fluoroquinolones (levofloxacin and moxifloxacin)
Complications
  •  Respiratory failure

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(M2.ID.17.4765) A 38-year-old female presents to the emergency department for cough. She reports that two days ago she developed a nonproductive cough with moderate shortness of breath. On review of systems, the patient also endorses chills and sweats as well as several episodes of diarrhea over the past three days. Her husband also reports that the patient seemed confused this morning when he spoke to her before he left for work. The patient’s past medical history is significant for diabetes mellitus type II for which she takes metformin and glipizide. She drinks 8-10 beers per week and has a 15 pack-year smoking history. She works as a sales manager at a local retail company. Her temperature is 102.6°F (39.2°C), blood pressure is 126/72 mmHg, pulse is 82/min, and respirations are 18/min. On physical exam, she is alert and oriented to person and place only. She has crackles bilaterally extending up to the mid-lung fields. Her abdomen is soft and non-distended without rebound or guarding. Laboratory testing is performed and reveals the following:

Serum:
Na+: 129 mEq/L
K+: 3.6 mEq/L
Cl-: 99 mEq/L
HCO3-: 17 mEq/L
Urea nitrogen: 16 mg/dL
Creatinine: 1.1 mg/dL

Leukocyte count: 16,300/mm^3
Hemoglobin: 13.2 g/dL
Mean corpuscular volume: 87 µm^3
Platelet count: 348,000/mm^3

A chest radiograph is performed and can be seen in Figure A. Which of the following is most likely to be elicited upon further questioning?

QID: 109039
FIGURES:
1

Risk factors for aspiration

10%

(3/29)

2

Recent travel to Arizona

7%

(2/29)

3

Exposure to incarcerated population

3%

(1/29)

4

Recent cruise travel

62%

(18/29)

5

Exposure to bird droppings

17%

(5/29)

M 6 D

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