Legionnaires' disease is a rare disorder that chiefly characterizes a chronic form of pneumonia causing severe lung inflammation due to an infection from a bacterium called legionella. This legionella bacterium was discovered in the year 1976, after an outbreak at a Philadelphia convention of the American Legion. Those who were infected developed a form of pneumonia that eventually came to be known as Legionnaires’ disease.

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This bacterium usually infects people via normal inhalation of contaminated droplets of water or soil. Although anyone can get infected with the legionella bacterium, older people and the ones with a weakened immune response are more susceptible to this infection. This bacterium can also lead to Pontiac fever, a milder version exhibiting several symptoms of the normal flu. Outbreaks of this disease have been chiefly reported due to water systems in hospital buildings and whirlpool spas in hotels and cruise ships. Although the underlying Pontiac fever may subside on its own, Legionnaire’s disease can be quite fatal in nature and may require a full course of antibiotics for proper treatment and management.

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legionnaire's disease


The main cause of Legionnaire’s disease is the Legionella pneumophila bacterium that mostly thrives well in warm water and moist soil. Although this bacterium rarely affects but when they thrive outdoors in water systems made by humans, such as home plumbing, air conditioners etc, they infect people speedily. Outbreaks due to this bacterium usually happen in closed complexes and large buildings that have a common waterbody that allows the bacterium to grow and multiply.

People commonly get infected by this bacterium by inhaling contaminated microscopic water droplets that are suspended in the air. Common locations where the legionella bacterium may thrive include:

  • Swimming pools
  • Birthing pools
  • Drinking water
  • Hot tubs and whirlpools
  • Public showers
  • Cooling towers in air conditioning systems
  • Hot water tanks and heaters
  • Decorative fountains
  • Natural bodies of water, such as lakes, rivers, and creeks

Apart from getting infected via the inhalation process, the infection can be transmitted in two other ways, including:

Aspiration: When you cough or choke while drinking water, if it is contaminated, the bacterium can enter the lungs accidentally and eventually infect and lead to Legionnaire’s disease.

Soil: One can even get infected with the Legionnaire’s disease while handling contaminated soil usually while working in garden, farming or using contaminated potting soil.

Risk Factors

Certain causative factors that increase the risk of Legionnaire’s disease includes:

Age:  Although this infection can happen to anyone, it usually affects people above the age of 50.

Health Anomalies: People already suffering from chronic lung infections or other severe conditions like diabetes, emphysema, kidney disease or cancer are more at risk of having Legionnaire’s disease.

Weakened Immunity: People having a compromised immunity due to some infection or disease like HIV/AIDS or those who are regularly consuming prescribed corticosteroids or organ transplant medications are more prone to getting infected with Legionella bacterium.

Unhealthy Habits: Those who have a habit of smoking cigarettes or taking any form of tobacco have an aggravated chance of getting lung infection.


The common signs and symptoms of Legionnaire’s disease usually start showing up within 2 to 14 days after getting exposed to the legionella bacterium. These include:

On or after the 2nd or 3rd day, people often start noticing more symptoms like:

  • Cough, accompanied with mucus and sometimes blood
  • Chills
  • Shortness of breath
  • Chest pain
  • Loss of appetite
  • Nausea
  • Vomiting
  • Diarrhea
  • Seizures
  • Confusion


If the infection is not treated on time, it can lead to several complications including:

  • Respiratory failure
  • Acute Kidney failure
  • Septic shock

Diagnosis And Treatment

On noticing any of the above-mentioned signs and symptoms, do consult a doctor right away to start the treatment at the earliest and avoid complications. The doctor usually does a thorough physical check-up, acknowledges the patients past medical history and conducts some diagnostics including:

  • Antigen test to look for the presence of antigens against the Legionella bacterium
  • Blood and Urine tests
  • Sampling of sputum and lung tissue
  • Imaging techniques like Chest X-ray


As soon as the infection is diagnosed, the doctor usually starts a course of antibiotics to manage the disease at hand. In some severe cases, the patient may require hospitalization for prompt medical care. In case, a person has a milder infection in the form of Pontiac fever, the symptoms subside on its own without treatment and doesn’t leave behind any side effects.