Legionnaires' disease: information for clinical team

Audience

Rapid guidance dissemination: 21/02/2025

Legionella is a bacteria spread by inhalation of aerosol.

Measures have been put in place to reduce this risk, but please consider Legionella in the differential for hospital acquired pneumonia (HAP) until further notice.

Clinical information

Incubation:

  • 2 to 14 days (commonly 5 to 6 days)

Risk factors for infection:

  • Can occur in previously well patients, increased risk in immunocompromised patients and smokers.

Clinical presentation:

Primarily pneumonia, important to note the pneumonia can present in atypical ways:

  • Diarrhoea and GI symptoms
  • Confusion
  • Hyponatraemia
  • Abnormal LFT’s
  • Cough, non productive/ small amount sputum

Actions for clinical assessment:

  • Bloods: FBC, U+E, LFT, CRP
  • Blood cultures, if indicated
  • Viral throat swab
  • Send urine (white top container) for Legionella Antigen
  • Send sputum and add ?legionella on the request form
  • Chest X-ray

Results from the urine antigen test should be available same day or next day.

  • A positive result confirms legionella, but a negative result does NOT exclude it.
  • If clinical suspicion, then treat with antibiotics empirically.

Treatment

Antibiotics: 

Legionella is covered by macrolides and quinolones.

Recommended empiric treatment of HAP with cover for legionella:

  • Add azithromycin: 500mg daily for 5 days to the standard Hospital acquired pneumonia (Antimicrobial) recommended treatment
    • If azithromycin is contraindicated, please discuss with Duty Consultant Microbiologist.
    • Note azithromycin is a QT prolonging drug.

Ie: empiric treatment of HAP

  • For non-severe HAP: patient will be on either co-trimoxazole PLUS azithromycin; or doxycycline PLUS azithromycin.
  • For severe HAP: patient will be on vancomycin plus aztreonam PLUS azithromycin

If patient is already on a quinolone (ciprofloxacin or levofloxacin), then azithromycin is NOT required.

Treatment of confirmed Legionella:

  • Confirmed cases should be discussed with Duty Microbiologist

Discussion of cases:

  • Please discuss with duty microbiologist cases where you have a high index of suspicion for Legionnaires' disease, or where you are unclear of the management.

We as a microbiology team are always happy to discuss if any concerns, and are available 24/7 via Raigmore switchboard

ABBREVIATIONS

  • CRP: Creatinine protein ratio
  • FBC: Full blood count
  • GI: Gastro-intestinal
  • HAP: Hospital acquired pneumonia
  • LFT: Liver function tests
  • QT: reference points on an electrocardiogram
  • U+E: Urine and electrolytes

Editorial Information

Last reviewed: 21/02/2025

Author(s): Microbiology, Infectious Disease Team.

Version: 1

Approved By: Rapid guidance dissemination: Awaiting approval

Reviewer name(s): Dr V. Plecko, Consultant Microbiologist.

Document Id: TAM677