Legionnaires’ disease (legionellosis) is a lung infection caused by the bacterium Legionella that thrive in warm, aquatic environments and are relatively resistant to the effects of chlorine and heat. Legionella are generally spread through the air by aerosolized water, which is then inhaled. Contaminated aerosols come from devices such as cooling towers, showers, faucets, spas, and decorative fountains.

Legionella most commonly causes one of two diseases:

  • Legionnaires’ disease is a type of severe pneumonia
  • Pontiac fever is mild illness that can include fever, muscle aches, and headaches
Transmission

The bacteria can become a health concern when they grow and spread in human-made building water systems, such as:

  • Showerheads and sink faucets
  • Hot tubs
  • Decorative fountains and water features
  • Large, complex plumbing systems
  • Cooling towers

Cooling towers are structures that contain water and a fan as part of centralized air-cooling systems for buildings or industrial processes.

Legionella is not transmitted from person to person.

Symptoms

Legionnaires’ disease symptoms usually develop 2-14 days after exposure to Legionella bacteria, but it can take longer. The symptoms of Legionnaires’ disease are similar to other types of pneumonia, including:

  • Cough
  • Fever
  • Headaches
  • Muscle aches
  • Shortness of breath

Signs of the disease can include a high fever, chills, and a cough. Some people also suffer from muscle aches and headaches. Gastrointestinal symptoms occur in 20-40% percent of cases.

A milder infection caused by the same type of Legionella bacteria is called Pontiac Fever. Symptoms are similar to Legionnaires’ disease with fever, headache, and muscle aches, however, there is no pneumonia and symptoms usually resolve without medical intervention.

Each year between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease in the U.S. Although the disease can occur at any time of year, the greatest number of illnesses are usually found in the summer and early fall.

Individuals Most At-Risk of Severe Illness

People most at risk of getting sick from infection with Legionella bacteria are individuals 50 or older, current or past smokers, and those who have a chronic lung disease (like emphysema).

People who have weak immune systems from diseases like cancer, diabetes, or kidney failure are also more likely to get sick when exposed to Legionella bacteria. People who take drugs that weaken the immune system (like after a transplant operation or chemotherapy) are also at higher risk.