Legionella pneumophila is a type of bacteria that can cause a severe form of pneumonia known as Legionnaires' disease. It is commonly found in warm water environments, such as hot tubs, cooling towers, and large plumbing systems. The bacteria thrive in temperatures between 20°C and 50°C (68°F to 122°F) and can spread through aerosolized water droplets. Infection occurs when a person inhales contaminated water vapor. Symptoms of Legionnaires' disease include cough, shortness of breath, fever, and muscle aches. While most healthy individuals are not at high risk, certain groups, such as the elderly or those with weakened immune systems, are more susceptible to severe illness.