Legionnaires' Disease is a severe form of pneumonia caused by the Legionella bacteria. These bacteria thrive in warm water environments, such as hot tubs, cooling towers, and large plumbing systems. People can become infected by inhaling mist or vapor containing the bacteria. Symptoms of Legionnaires' Disease include cough, shortness of breath, fever, and muscle aches. It primarily affects older adults, smokers, and individuals with weakened immune systems. Diagnosis is typically made through laboratory tests, and treatment usually involves antibiotics to combat the infection.