The bacteria can be found in shower heads and faucets, hot tubs, cooling towers, hot water tanks, decorative fountains or plumbing systems in large buildings.
People breathe in small droplets of water that contain the bacteria, the CDC says.
Symptoms are a cough, shortness of breath, high fever, muscle aches and headaches. The symptoms begin two to 10 days after exposure.
"In general. A doctor wants to check for pneumonia and or urine or a phlegm." Legionnaires' disease to other people, "the CDC says. The Mayo Clinic says you can not get it from person-to-person contact.
How many people from Legionnaires '?
About one in 1
How many cases are there a year?
About 7,500 US cases of Legionnaires' disease were reported to the CDC in 2017, the agency said, adding that it is likely to be underestimated because of the illness underdiagnosed. 550% since 2000.
There are a variety of factors in the rising number of cases, including a true increase in people getting the disease because of more at-risk people But so because of increased reporting. 
How do we prevent it?
There are no vaccines that prevent Legionnaires' disease. Instead, according to the CDC, Legionnaires' disease can be prevented by making sure that "building owners and managers maintain building water systems in order to reduce the risk of legionella growth and spread."
Who is most at risk
People 50 or older, current or former smokers and people with chronic lung disease or weak immune systems. The Mayo Clinic says. "
There is an outbreak at American Legion Convention in Philadelphia in 1976. The CDC said 29 people died and 180 people got sick at the conventional hotel.