Legionnaires' disease is a severe form of pneumonia — lung inflammation usually caused by infection. It's caused by a bacterium known as legionella.
Most people catch Legionnaires' disease by inhaling the bacteria from water or soil. 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. 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 have 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 can 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 — can produce 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, such as smokers or older adults, 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. However, legionella bacteria can multiply in water systems made by humans, such as air conditioners.
Although it's possible to get Legionnaires' disease from home plumbing, most outbreaks have occurred in large buildings, perhaps because complex systems allow the bacteria to grow and spread more easily. Also, home and car air conditioning units don't use water for cooling.
Most people become infected when they inhale microscopic water droplets containing legionella bacteria. This might be from the spray from a shower, faucet or whirlpool, or water from the ventilation system in a large building. Outbreaks have been linked to:
Besides by breathing in 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 can be a problem in hospitals and nursing homes, where germs can spread easily and people are vulnerable to infection.
Legionnaires' disease can lead to a number of life-threatening complications, including:
When not treated promptly, Legionnaires' disease can be fatal.
Outbreaks of Legionnaires' disease are preventable, but prevention requires water management systems in buildings that ensure that water is monitored and cleaned regularly.
To lower your personal risk, avoid smoking.
Legionnaires' disease is similar to other types of pneumonia. To help identify the presence of legionella bacteria quickly, your doctor might use a test that checks your urine for legionella antigens — foreign substances that trigger an immune system response. Other tests might include:
Legionnaires' disease is treated with antibiotics. The sooner therapy is started, the less likely the chance of developing serious complications. In many cases, treatment requires hospitalization. Pontiac fever goes away on its own without treatment and causes no lingering problems.
You're likely to start by seeing your family doctor. In some cases, you might be referred to a doctor who specializes in treating lung disease (pulmonologist) or infectious diseases, or you might be advised to go to an emergency department.
Make a list of:
Bring a family member or friend along, if possible, to help you remember the information your doctor provides.
Questions you might ask your doctor include:
Don't hesitate to ask other questions.
Your doctor is likely to ask you questions, including:
To avoid making your condition worse, follow these tips:
If you get sicker before you see a doctor, go to an emergency room.
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