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legionella

Legionella (Legionaire's disease)

introduction

  • gram negative, aerobic clinically important bacteria
  • Legionella pneumophila
    • an aquatic organism mainly thriving in the cooling system of air conditioning towers at temperatures of 25-45°C, and is responsible for >90% of cases of potentially fatal Legionellossis (Legionaire's disease) and the milder form, Pontiac fever.
    • these conditions usually develop in local outbreaks resulting from aerosol inhalation from contaminated air conditioning units on buildings.
    • they can survive water temperatures of 50°C but die after decreasing duration of exposure to temperatures above 55°C, such that by 66°C they die with only 2 minutes exposure at that temperature.
    • they are dormant below 20°C
  • Legionella longbeachae
    • is common in potting mix and may cause pneumonia after gardeners inhale the particles such as when opening the bag or from inhaling water droplets from hanging baskets
    • prevention: wear P2 masks and gloves when using potting mix, open bag away from face, wash hands after
    • it is particularly common in Australia
    • see also:

risk factors for infection

  • type and intensity of aerosol exposure
  • elderly (age > 50yrs)
  • smoker
  • chronic heart or lung disease
  • immunosuppression

clinical features of Legionaire's disease

"severe disease"

  • respiratory failure
  • bilateral pneumonia
  • rapidly worsening pulmonary infiltrates, or,
  • the presence of at least 2 of the following 3 characteristics:
    • uraemia
    • diastolic BP < 60mmHg
    • RR > 30/min

ED Mx of suspected Legionaire's disease

  • ABC's as usual
  • iv access
  • bloods for FBE, U&E, LFT's, phosphate, blood cultures, serology (but will need paired samples 4-8 weeks apart)
  • MSU for
    • urinary Legionella antigens (only detects serogroup 1 though?) - 80% sensitive on days 1-3 of illness
    • urinary PCR (detects other serogroups than only serogroup 1)
  • sputum culture, PCR +/- DFA
  • CXR
  • delay in antibiotic Rx significantly increases the risk of mortality.
  • include empiric anti-Legionella therapy in the regimen for severe CAP and in specific cases of nosocomial pneumonia.
  • doxycycline, azithromycin, macrolides, and quinolones are more active against LD than erythromycin.
  • for severe disease, a fluoroquinolone is recommended
  • most patients require admission
  • contact Infectious Diseases unit of the hospital for further advice
  • LD is a notifiable disease
  • most previously healthy patients respond to Rx within 3-5 days
legionella.txt · Last modified: 2019/12/13 00:51 (external edit)