Legionnaire’s disease is a type of pneumonia that can develop after exposure to Legionella bacteria.

What is Legionnaire’s disease?

Legionnaire’s disease is a type of pneumonia caused by a group of bacteria called Legionella. Most healthy people exposed to Legionella do not get sick, but Legionnaire’s disease can be serious, especially in older adults or those with weakened immune systems.

What causes Legionnaire’s disease?

Legionnaire’s disease is caused by Legionella bacteria. After the bacteria are inhaled, they can infect the lungs and cause pneumonia.

How is Legionnaire’s disease spread?

Legionnaire’s disease is spread by tiny water droplets contaminated with Legionella bacteria. Legionnaire’s disease does not spread from person-to-person.

Legionella bacteria can be found in nature, but the greatest risk of infection comes from man-made water systems, where the bacteria can thrive. Potential sources of Legionella include:

• Hot tubs
• Fountains
• Shower heads
• Swimming pools
• Large air-conditioning units (especially those with cooling towers)
• Plumbing systems

Legionella bacteria can also grow in soil. This type of transmission is most common in Australia and New Zealand but much rarer in other parts of the world.

Legionnaire’s Disease and Air Conditioning

Large air-conditioning systems (like those often used in hotels, hospitals and high-rise buildings) have been linked to outbreaks of Legionnaire’s disease. This is because those large systems use cooling towers filled with water to remove heat. If not properly maintained, the water can foster Legionella bacteria, which can then be swept into the system’s fans and circulated throughout the building’s air.

Luckily, you don’t need to worry about your home’s AC system. Smaller air-conditioning systems (like those installed in homes or used as window AC units) do not use water and therefore do not pose a risk. Similarly, your car’s AC system relies on a particular type of refrigerant (which cannot be contaminated by Legionella) to cool.

In contrast, you may still be at risk if you stay at a hotel or work in an office building with improperly maintained cooling towers.

Legionnaire’s Disease Symptoms

Symptoms typically develop between two and 10 days of exposure to Legionella bacteria. Symptoms include:

• Fever
• Cough
• Shortness of breath
• Nausea
• Vomiting
• Diarrhea

When should I see a doctor?

Legionnaire’s disease is a serious condition, so see your doctor immediately if you think you might have it. Treatment is more successful when Legionnaire’s disease is diagnosed and treated early.

If you have trouble breathing or a high fever, go to the emergency room.

How is Legionnaire’s disease diagnosed?

Your doctor can diagnose Legionnaire’s disease with a urine sample, which will detect Legionella bacteria antigens. The disease can also be diagnosed by testing respiratory secretions.

Your doctor may also request a chest X-ray or CT scan of your chest to examine your lungs and confirm that you have pneumonia.

Legionnaire’s Disease Risk Factors

Not everyone exposed to Legionella bacteria gets sick, but certain individuals are most at risk of developing Legionnaire’s disease and experiencing complications. Risk factors include:

• Older age (>50)
• Having a weakened immune system
• Smoking
• Chronic respiratory disease
• Heart disease
• Kidney disease
• Diabetes
• Cancer

Legionnaire’s Disease Complications

Legionnaire’s disease can lead to respiratory failure and even death. Fortunately, most people recover quickly with treatment.

Legionnaire’s Disease Treatment

Legionnaire’s disease is treated with antibiotics, which kill the Legionella bacteria. The most commonly used antibiotics are levofloxacin and azithromycin. If you are severely ill, these medications will be given intravenously.

Some patients with respiratory failure require mechanical ventilation in an intensive care unit to provide high oxygen concentrations or assist with tiring respiratory muscles.

Preventing Legionnaire’s Disease

Legionnaire’s disease can be prevented by limiting the spread of Legionella bacteria. This requires proper maintenance of water systems. Learn more from the Centers for Disease Control and Prevention about preventing waterborne bacteria, like Legionella, at home.