Legionnaires disease, or Legionellosis is an infection caused by the inhalation of airborne water droplets contaminated by Legionella pneumophila & other bacteria of the family Legionellaceae.

There are more than 50 identified species of Legionella and about 70 serogroups, with Legionella pneumophila (SG1 and SG2) being the species causing more than 80% of the detected cases of the disease.

L.pneumophila causes Legionellosis including:

  • A pneumonia-type illness called Legionnaires disease
  • And a mild-flu like illness called Pontiac Fever

Pontiac Fever and the more severe Legionnaires disease are caused by the same bacteria. Pontiac Fever does not include pneumonia.

The History of Legionnaires Disease

Legionella was first identified in 1976 when 34 people attending a gathering of an American Legion died and 221 contracted Legionella at the Bellevue Stratford Hotel in Pennsylvania, USA.

The most significant outbreak in Australia to date was at Melbourne Aquarium in April 2000. There were 101 cases of Legionnaires disease and four fatalities. The outbreak was blamed on the aquarium’s cooling towers. However, more recent outbreaks in Queensland, Australia include warm water systems in hospitals and also ice machines as the source of the bacteria.

Studies from the UK show that

  • approximately 3% of pneumonia is caused by Legionella
  • 25% of Legionella cases occur in hospitalised patients
  • the mortality rate can be as high as 40% in hospital settings
  • 80% of Legionella cases comprise aged patients that are immuno-compromised

Empirical data shows that certain risk groups exist. It appears that males over the age of 50 are three times more susceptible to the disease, whereas children are rarely infected.

People with an existing respiratory disease, smokers and people with a suppressed immune system (due to age, cancer, diabetes, recent surgery, alcoholism etc.) are especially at risk, which is why hospitals and nursing homes need special attention when it comes to Legionella.

How To Prevent Legionnaires Disease