Legionnaires' Disease / Legionellosis

DISEASE NAME:

Legionnaires' Disease / Legionellosis

Respiratory

Legionnaires' Disease / Legionellosis

Legionnaires’ disease is an uncommon, severe type of pneumonia caused by Legionella bacteria, often requiring intensive care treatment in hospital. Legionellosis can be fatal and death can occur in approximately 10-15% of otherwise healthy people.

A mild form of Legionnaires' disease, known as Pontiac fever, may produce signs and symptoms including a fever, chills, headache and muscle aches. Pontiac fever doesn't infect your lungs, and symptoms usually clear within two to five days.

Legionella bacteria are found in many types of water systems. The bacteria multiply in warm, and stagnant water, such as can be found in air conditioning cooling towers, certain plumbing systems especially showers, spa pools, decorative fountains, sprinklers and nebulisers. The infection is spread through the air from the water source. People become infected when they breathe in aerosols (tiny droplets of water) which have been contaminated with Legionella bacteria. There is no evidence of spread from person-to-person. A type of Legionella bacteria has also been found in potting compost, particularly in warm countries, and gardeners can be infected by breathing in the bacteria through water droplets, dust or from hands contaminated with compost. Legionellosis is very uncommon, with low numbers of infections notified every year in Ireland. Legionellosis is a notifiable disease in Ireland.

Last updated: 21 March 2024

Checklists

Legionnaires' Disease - Checklist for hostels providing accommodation for people who are homeless

17, Jun 2016
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Case Definitions

Clinical criteria
Legionnaires’ disease
Any person with pneumonia
Pontiac fever
A self limiting influenza like illness characterised by fever, headache, myalgia and non-productive cough. Patients recover spontaneously without therapy after 2-5 days. No signs of pneumonia. Pontiac fever is frequently associated with Legionnaires’ disease outbreaks.

Laboratory criteria
- Laboratory criteria for case confirmation

At least one of the following three:
- Isolation of Legionella spp. from respiratory secretions or any normally sterile site
- Detection of Legionella pneumophila antigen in urine
- Significant rise in specific antibody level to Legionella pneumophila serogroup 1 in paired serum samples

- Laboratory criteria for a probable case

At least one of the following four:
- Detection of Legionella pneumophila antigen in respiratory secretions or lung tissue e.g. by DFA staining using monoclonal-antibody derived reagents
- Detection of Legionella spp. nucleic acid in respiratory secretions, lung tissue or any normally sterile site
- Significant rise in specific antibody level to Legionella pneumophila other than serogroup 1, or other Legionella spp. in paired serum samples
- Single high level of specific antibody to Legionella pneumophila serogroup 1 in serum

Epidemiological criteria
NA

Case classification
A. Possible case
NA
B. Probable case
Any person meeting either of the clinical criteria AND at least one laboratory criterion for a probable case
C. Confirmed case
Any person meeting either of the clinical criteria AND at least one laboratory criterion for a confirmed case

Current as of: 22 January 2019