Legionnaires' disease

Introduction

Legionnaires’ disease is a potentially fatal lung infection (pneumonia) that is caused by the legionella bacteria. Legionnaires’ disease is caught by breathing in small droplets of contaminated water. It is not contagious and cannot be spread directly from person to person.

Initial symptoms include a high fever and muscle pain. Once the bacteria begin to infect your lungs, you may also develop a persistent cough (see Legionnaires disease - symptoms). Prompt treatment using antibiotics is essential to reduce the risk of death. See Legionnaires’ disease - treatment for more information.

The condition is called Legionnaires’ disease because it was first identified after a mass outbreak at a hotel hosting a convention of a veteran organisation known as the American Legion.

Causes of Legionnaires’ disease

Legionella bacteria is commonly found (often in low numbers) in sources of water, such as rivers and lakes. The bacteria sometimes find their way into artificial water supply systems such as:

  • air conditioning systems
  • hot and cold water services
  • cooling towers

Given the right conditions, legionella bacteria can rapidly spread and contaminate these water systems.

Large buildings, such as hotels, hospitals, museums and office blocks, are more vulnerable to legionella contamination because they have larger, more complex water supply systems in which legionella contamination can quickly spread.

There are strict regulations regarding the maintenance and control of water supply systems, such as either keeping the water cooled below 20ºC (68ºF) or heated above 60ºC (140ºF) to prevent an outbreak of Legionnaires’ disease.

See Legionnaires’ disease - causes for more information about where legionella bacteria can be found and how they can spread.

How common is Legionnaires’ disease?

The actual number of cases of Legionnaires’ disease may be much higher than the reported number of cases. This is because not everyone with pneumonia may have the relevant test for Legionnaire’s disease, particularly those with milder symptoms. Therefore, these cases may not be reported to the health authorities.

Legionnaires’ disease is three times more common in men than women, and it mostly affects people who are over 50 years old.

Outlook

Legionnaire’s disease can be very serious, particularly in vulnerable people, such as the elderly or people with pre-existing health conditions.

An estimated 10-15% of otherwise healthy people who contract Legionnaires’ disease will die. The number of deaths may be higher in people with pre-existing health conditions, such as a weakened immune system (the body’s natural defence against illness and infection).

Last updated: 06 June 2012

Continue to next section: Symptoms of Legionnaires' disease