Legionnaires’ Disease is a severe form of pneumonia caused by the Legionella bacteria. It was first identified in 1976 when an outbreak occurred during an American Legion convention in Philadelphia – hence the name.

Legionnaires’ Disease is also known as Legionellosis: This term encompasses both Legionnaires’ Disease and Pontiac fever, both are caused by the Legionella bacteria. Pontiac fever is a milder illness which typically presents with flu-like symptoms.

What causes Legionnaires’ Disease?

The disease is primarily contracted by inhaling small droplets of water contaminated with Legionella bacteria.

These bacteria thrive in warm water environments, especially those with stagnant water or poor maintenance. Common sources of Legionella contamination include hot water tanks, cooling towers, plumbing systems, and decorative fountains.

Transmission of Legionnaires’ Disease

When a person inhales droplets of water containing legionella,  the bacteria enter the lungs and infect the respiratory system, leading to pneumonia.

How do people usually catch Legionnaires’ Disease?

The transmission of Legionnaires’ Disease can occur in various ways.

Inhalation of contaminated water droplets is the most common route of transmission, but it can also be contracted by aspiration of contaminated water (such as while drinking or swallowing).

Person-to-person transmission is extremely rare, and the disease cannot be contracted by touching or being near an infected person.

Symptoms of Legionnaires’ Disease

The symptoms of Legionnaires’ Disease are similar to those of other types of pneumonia and can vary in severity.

Common symptoms include high fever, cough, shortness of breath, muscle aches, headaches, and chest pain. Some individuals may also experience gastrointestinal symptoms such as diarrhoea and vomiting.

Are there any risk factors?

Risk factors (i.e. things that make it worse or make you more susceptible to it) include:

  • Weak immune system
  • Age – people above 50 years or older are more vulnerable to the infection
  • Having conditions such as emphysema, diabetes, kidney disease, cancer, pulmonary-related illness, immuno-suppression, or chronic respiratory or renal illnesses
  • Smoking, a history of heavy drinking

How do we test for it?

Diagnosis of Legionnaires’ Disease can be challenging since the symptoms resemble other respiratory infections. A doctor will typically perform a series of tests including a physical examination, chest X-ray, and laboratory tests to identify the presence of Legionella bacteria.

If caught, how is Legionnaire’s Disease treated?

Prompt treatment is essential for individuals diagnosed with Legionnaires’ Disease, as the condition can be life-threatening.

Antibiotics are commonly prescribed to combat the infection. In severe cases, hospitalisation may be required to provide supportive care, such as oxygen therapy and intravenous fluids.

The effectiveness of treatment depends on early detection and the overall health of the individual.

Prevention measures for Legionnaires’ Disease

Preventing Legionnaires’ Disease requires a comprehensive approach to minimise the risk of Legionella bacteria growth and transmission. Some key prevention measures include:

  • Regular maintenance and cleaning of hot water tanks, plumbing systems, and cooling towers to prevent bacterial growth
  • Ensuring proper disinfection and circulation of water in hot tubs, spas, and decorative fountains
  • Regularly monitoring and adjusting the temperature of hot water systems to discourage bacterial growth
  • Implementing water management plans in large buildings, hospitals, and healthcare facilities to control Legionella contamination
  • Educating individuals on the risk factors associated with Legionnaire’s Disease and promoting good hygiene practices

By implementing these prevention measures, the risk of Legionella contamination can be significantly reduced, thereby preventing outbreaks and protecting public health.


Understanding Legionnaires’ Disease and its causes, symptoms, and prevention measures is crucial in protecting ourselves and others from this potentially life-threatening illness. Find out more about protecting people from Legionnaires’ Disease here or with our Legionella Awareness Course.

Published On: April 23rd, 2024