BATON ROUGE — Legionnaires' disease is a serious lung infection caused by Legionella bacteria. Most people exposed to the bacteria don't get sick, but some people are at higher risk.

"Legionnaires' disease is a type of serious pneumonia that people can get typically from exposure to mist or water," Mayo Clinic's Nipunie Rajapakse, an infectious disease doctor, said.

Rajapakse says it's not spread person-to-person.

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

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," Rajapakse said.

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," Rajapakse said.

It can take two to four days after exposure to feel symptoms.

"Symptoms of Legionnaires disease can start as a flu-like illness with fever, body aches, cough, malaise...then it can present like pneumonia," Rajapakse said.

It can progress to severe illness requiring hospitalization.

"But when identified and treated early, it is treatable with antibiotics," Rajapakse said.