Legionella infection is acquired by inhalation of aerosolized bacteria or, rarely, microaspiration of contaminated drinking water.
Presentation includes respiratory symptoms such as cough (may not be productive) and shortness of breath, fever, chills, and chest pain. Other symptoms include headache, nausea, vomiting, abdominal pain, or diarrhea.
Definitive diagnosis is made with a positive laboratory test.
First-line treatment is with a fluoroquinolone or a newer-generation macrolide.
Complications are the same as those for pneumonia and include respiratory failure, parapneumonic effusion, empyema, lung abscess, and death.
Legionella are gram-negative rod bacteria with at least 20 pathogenic species and 70 serogroups. Legionella reproduce intracellularly, including within macrophages, which paradoxically protect them as they replicate.Legionella pneumonia, known as Legionnaires' disease, occurs when the bacteria are inhaled (or rarely aspirated) into the lungs. Nonpneumonic Legionella infection is known as Pontiac fever.
History and exam
Key diagnostic factors
- known acquaintance with Legionella
Other diagnostic factors
- productive cough
- abdominal pain
- non-municipal water supply
- recent residential plumbing repair
- cytotoxic chemotherapy
- 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
1st investigations to order
- complete metabolic profile
- chest x-ray
- urine antigen detection of Legionella pneumophila serogroup 1
- sputum Gram stain
Investigations to consider
- Legionella pneumophila serology
- direct fluorescent antibody (DFA) assay
- Legionella pneumophila polymerase chain reaction (PCR)
mild/moderate Legionella pneumonia
severe Legionella pneumonia
Forest W. Arnold, DO, MSc, FIDSA
Associate 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.
Victor L. Yu, MD
Professor of Medicine
University of Pittsburgh
VLY declares that he has no competing interests.
- Coronavirus disease 2019 (COVID-19)
- Bacterial pneumonia
- Hospital-acquired pneumonia
- Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults
Community-acquired pneumonia severity index (PSI) for adults
CURB-65 pneumonia severity scoreMore Calculators
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