Legionnaires’ disease is a severe form of pneumonia — lung inflammation usually caused by infection. Legionnaires’ disease is caused by a bacterium known as legionella.
You can’t catch legionnaires’ disease from person-to-person contact. Instead, most people get legionnaires’ disease from inhaling the bacteria. Older adults, smokers and people with weakened immune systems are particularly susceptible to legionnaires’ disease.
The legionella bacterium also causes Pontiac fever, a milder illness resembling the flu. Separately or together, the two illnesses are sometimes called legionellosis. Pontiac fever usually clears on its own, but untreated legionnaires’ disease can be fatal. Although prompt treatment with antibiotics usually cures legionnaires’ disease, some people continue to experience problems after treatment.
Legionnaires’ disease usually develops two to 10 days after exposure to legionella bacteria. It frequently begins with the following signs and symptoms:
By the second or third day, you’ll develop other signs and symptoms that may include:
Although legionnaires’ disease primarily affects the lungs, it occasionally can cause infections in wounds and in other parts of the body, including the heart.
A mild form of legionnaires’ disease — known as Pontiac fever — may produce signs and symptoms including a fever, chills, headache and muscle aches. Pontiac fever doesn’t infect your lungs, and symptoms usually clear within two to five days.
See your doctor if you think you’ve been exposed to legionella bacteria. Diagnosing and treating legionnaires’ disease as soon as possible can help shorten the recovery period and prevent serious complications. For people at high risk, prompt treatment is critical.
The bacterium Legionella pneumophila is responsible for most cases of legionnaires’ disease. Outdoors, legionella bacteria survive in soil and water, but rarely cause infections. Indoors, though, legionella bacteria can multiply in all kinds of water systems — hot tubs, air conditioners and mist sprayers in grocery store produce departments.
Although it’s possible to contract legionnaires’ disease from home plumbing systems, most outbreaks have occurred in large buildings, perhaps because complex systems allow the bacteria to grow and spread more easily.
Most people become infected when they inhale microscopic water droplets containing legionella bacteria. This might be the spray from a shower, faucet or whirlpool, or water dispersed through the ventilation system in a large building. Outbreaks have been linked to a range of sources, including:
Although legionella bacteria primarily spread through aerosolized water droplets, the infection can be transmitted in other ways, including:
Not everyone exposed to legionella bacteria becomes sick. You’re more likely to develop the infection if you:
Legionnaires’ disease is a sporadic and local problem in hospitals and nursing homes, where germs may spread easily and people are vulnerable to infection.
Legionnaires’ disease can lead to a number of life-threatening complications, including:
When not treated effectively and promptly, legionnaires’ disease may be fatal, especially if your immune system is weakened by disease or medications.
Outbreaks of legionnaires’ disease are preventable, but prevention requires meticulous cleaning and disinfection of water systems, pools and spas.
Avoiding smoking is the single most important thing you can do to lower your risk of infection. Smoking increases the chances that you’ll develop legionnaires’ disease if you’re exposed to legionella bacteria.