Photo used for illustrative purposes.

Legionnaires' disease is a serious lung infection caused by Legionella bacteria. While most people exposed to the bacteria don't get sick, some people are at higher risk of infection and potentially serious illness.

Dr. Nipunie Rajapakse, a Mayo Clinic infectious disease expert, explains how this disease is spread and what you should know about Legionnaires' disease.

"Legionnaires' disease is spread through inhaling mist that has the Legionella bacteria in it," says Dr. Rajapakse.

"That mist can come from many different sources that use water. The more common places that we see outbreaks associated are whirlpools, air conditioning units or fountains," she says.

Home and car air conditioning units aren't a risk for Legionella growth because they don't use water to cool the air.

Not everyone exposed gets sick, but some people are more susceptible to illness than others.

"Certain people might be at more risk of getting Legionnaires' disease; we definitely see it more commonly in older individuals or people who have weakened immune systems," says Dr. Rajapakse.

It can take 2 to 4 days after exposure to feel symptoms.

"Symptoms of Legionnaires' disease can start as a flu-like illness with fever, body aches, cough, malaise, kind of feeling really tired; then [it] can present like pneumonia," she says.

It can progress to severe illness requiring hospitalization.

Although the infection primarily affects the lungs, occasionally, it can cause infections in wounds and in other parts of the body, including the heart.

"When identified and treated early, it is treatable with antibiotics," says Dr. Rajapakse.

Tribune News Service