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Legionnaires’ disease

A guide to aerosol exposure from building water systems, pneumonia differentiation, paired testing, and appropriate antibiotics.

Legionnaires' disease · legionellosis

MONDO:0005824Public QA completeSource-bound · 4

Disease at a glance

Start with the essentials, then explore the patient and research views.

Public revision · 0477f4e9ac10

Disease class
Legionnaires' disease is pneumonia caused by Legionella bacteria.
Core mechanism
Infection can follow inhalation of aerosols or aspiration of water containing amplified Legionella.
Genes or cause
It generally does not spread from person to person.
Typical features
Fever, cough, dyspnea, myalgia, and headache occur, sometimes with gastrointestinal or neurologic symptoms.
Variability
Older age, smoking, chronic lung disease, immunosuppression, and recent healthcare exposure increase risk.
Diagnosis
Clinical features or chest imaging alone cannot distinguish it from pneumonia caused by other pathogens.
Management
Diagnosis is supported by urinary antigen testing paired with culture or molecular testing of a lower-respiratory specimen.
Treatment and research
The urinary antigen test mainly detects L. pneumophila serogroup 1 and can miss other species or serogroups.
Reading evidence
Treatment uses a macrolide or respiratory fluoroquinolone active against Legionella.
Key caution
Appropriate antibiotic treatment should not be delayed solely to obtain diagnostic specimens.

For patients and families

A structured guide for understanding the disease and preparing for clinical conversations.

At a glance

Legionnaires' disease is pneumonia caused by Legionella bacteria.

Fever, cough, dyspnea, myalgia, and headache occur, sometimes with gastrointestinal or neurologic symptoms.

How the disease works

Infection can follow inhalation of aerosols or aspiration of water containing amplified Legionella.

It generally does not spread from person to person.

Why experiences vary

Older age, smoking, chronic lung disease, immunosuppression, and recent healthcare exposure increase risk.

Diagnosis and management

Clinical features or chest imaging alone cannot distinguish it from pneumonia caused by other pathogens.

Treatment status

Diagnosis is supported by urinary antigen testing paired with culture or molecular testing of a lower-respiratory specimen.

The urinary antigen test mainly detects L. pneumophila serogroup 1 and can miss other species or serogroups.

Reading clinical trials

Healthcare- or travel-associated cases may require public-health investigation and assessment of building-water exposure sources.

Topics for a clinical visit

Clinical discussion should cover severity, travel, healthcare and water exposure, paired testing, antibiotic coverage, and public-health reporting.

Medical notice

This material is for disease education and is not a personal diagnosis or treatment instruction.

Evidence and sources

A trial registry status does not establish efficacy or regulatory approval.