Legionella (Legionaire's disease)

see also:

• clinically important bacteria
• pneumonia

• 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:
    • wikipedia

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

• incubation 2-10 days
• fever > 40°C
• cough - dry or productive
• chest pain - may be non-pleuritic
• tachypnoea
• localised rales
• CXR:
  • rapidly progressive asymmetrical infiltrates are characteristic
  • 50% have patchy alveolar infiltrates
  • 25% have interstitial infiltrates
  • 1/3rd develop pleural effusions
  • abnormalities may take up to 3-4 months to resolve completely
• headache
• lethargy
• relative bradycardia
• watery diarrhoea
• nausea, vomiting, abdominal pain
• mild myalgia
• mental state changes progressing to encephalopathy
• may develop:
  • myocarditis
  • infective endocarditis (including SBE) if prosthetic valves
  • pancreatitis
  • acute kidney injury (AKI) / acute renal failure (ARF)
  • hypophosphataemia
  • hyponatraemia which is reasonably specific to LD
  • high C reactive protein (CRP), erythrocyte sedimentation rate (ESR), ferritin
  • microhaematuria, proteinuria
  • elevated LFTs

• 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

• 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