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Legionella infection

Last reviewed: 28 Oct 2023
Last updated: 15 Sep 2023



History and exam

Key diagnostic factors

  • known acquaintance with Legionella
  • fever
  • headache
  • crackles/rhonchi
More key diagnostic factors

Other diagnostic factors

  • productive cough
  • dyspnea
  • nausea/vomiting
  • abdominal pain
  • hypoxia
  • tachycardia
Other diagnostic factors

Risk factors

  • non-municipal water supply
  • recent residential plumbing repair
  • smoking
  • cytotoxic chemotherapy
  • corticosteroids
  • electric water heater
  • working >40 hours per week
  • recent travel
  • diabetes mellitus
  • professional driver
  • use of whirlpool spas
  • living close to a cooling tower
  • filling nebulizer, humidifiers, ventilator tubing, or lavage equipment with tap water
  • close proximity to a decorative fountain
  • consumption of Legionella pneumophila-contaminated ice
  • delivery by water birth
  • exposure to contaminated compost
  • exposure to rainwater
More risk factors

Diagnostic investigations

1st investigations to order

  • CBC
  • complete metabolic profile
  • chest x-ray
  • urine antigen detection of Legionella pneumophila serogroup 1
  • sputum Gram stain
  • cultures
More 1st investigations to order

Investigations to consider

  • Legionella pneumophila polymerase chain reaction (PCR)
  • Legionella pneumophila serology
More investigations to consider

Treatment algorithm


mild/moderate Legionella pneumonia

severe Legionella pneumonia or no response to initial therapy



Forest W. Arnold, DO, MSc, FIDSA
Forest W. Arnold

Professor of Medicine

Division of Infectious Diseases

Department of Medicine

School of Medicine

University of Louisville




FWA declares that he has no competing interests.


Dr Forest W. Arnold would like to gratefully acknowledge Dr Allen Griffin, a previous contributor to this topic.


AG declares that he has no competing interests.

Peer reviewers

Victor L. Yu, MD

Professor of Medicine

University of Pittsburgh




VLY declares that he has no competing interests.

  • Legionella infection images
  • Differentials

    • Coronavirus disease 2019 (COVID-19)
    • Bacterial pneumonia
    • Hospital-acquired pneumonia
    More Differentials
  • Guidelines

    • Pneumonia in adults: diagnosis and management
    • Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults
    More Guidelines
  • Calculators

    Community-acquired pneumonia severity index (PSI) for adults

    CURB-65 pneumonia severity score

    More Calculators
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