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Legionellosis (Legionella)

What is Legionella?

Legionella is a type of bacteria that is naturally found in freshwater environments, such as lakes and streams. However, Legionella bacteria can grow and spread in human-made water systems or devices that use water. These water systems and devices can include:

  • Showerheads and sink faucets
  • Hot tubs
  • Decorative fountains and water features
  • Hot water tanks
  • Large, complex plumbing systems
  • Cooling towers (which use water to cool air as part of centralized air conditioning systems for buildings or industrial processes)

Small water droplets or mist from these sources can contain Legionella bacteria, which people can breathe in without knowing, sometimes causing infection in the lungs. 

Legionella can be present in water at many places where people live, work and play. For this reason, it can be difficult to avoid breathing in water droplets containing Legionella. Although Legionella can cause serious infections in people who are at high risk for lung infections, most healthy people who are exposed to Legionella don’t get sick.

Transmission: Legionella grow in natural/human-made water systems. Legionella aerosolize and are inhaled; infection can occur. 

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What is legione​​​llosis? 

Legionellosis is the general name given to infections that are caused by Legionella bacteria. There are two types of legionellosis: Legionnaires’ disease (a serious form of pneumonia) and Pontiac fever (a milder illness). Most commonly, legionellosis is caused by breathing in mist or small droplets of water that contain Legionella bacteria. In general, legionellosis does not spread from person to person. 

Legionnaires’ Disease

Legionnaires’ disease is a severe type of lung infection or pneumonia. Legionnaires’ disease often requires hospital care, though it can usually be treated successfully with antibiotics. Symptoms of Legionnaires’ disease are similar to other types of pneumonia and can include:

  • Cough
  • Shortness of breath
  • Fever
  • Chills
  • Headaches
  • Muscle aches
  • Nausea
  • Vomiting
  • Diarrhea​
  • Confusion​​​​

Most healthy people exposed to Legionella do not develop Legionnaires’ disease. But some people are at higher risk of getting Legionnaires’ disease, including:

  • Adults over the age of 50
  • Current and former smokers
  • People with certain health conditions, such as:
    • Chronic lung disease (including COPD and emphysema)
    • Cancer
    • Diabetes
    • Kidney or liver failure
    • Treatment with medication that weakens the immune system (including chemotherapy and medicine taken after organ transplant)​

People at risk for Legionnaires’ disease can help prevent infection by reducing their exposure to recreational or decorative water sources where Legionella could be a concern. These include:

  • Hot tubs
  • Misters and decorative water fountains
  • Showers outside the home, such as at gyms, spas, or recreation centers​​

Because it can be difficult to avoid breathing in mist or water droplets that could contain Legionella, the key to preventing Legionnaires’ disease is to reduce the growth and spread of Legionella in the first place.

​Learn more about preventing waterborne germs at home

​Pontiac Fever

Pontiac fever is a milder infection that gets better on its own. Symptoms of Pontiac fever can include fever and muscle aches but does not include pneumonia (lung infection). Symptoms of Pontiac fever usually get better in less than a week and do not require medical care. ​​​

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