Wellness Health & Well-being Legionnaires' Disease: What You Need to Know By Mary Jo DiLonardo Senior Writer University of Cincinnati Mary Jo DiLonardo covers a wide range of topics focused on nature, health, science, and anything that helps make the world a better place. our editorial process Mary Jo DiLonardo Updated July 17, 2019 The bacteria that causes Legionnaires' disease can be spread in water droplets from a fountain spray. nasyafar/Shutterstock Share Twitter Pinterest Email Wellness Health & Well-being Clean Beauty There's something nefarious about Legionnaires' disease. This serious type of pneumonia is caused by bacteria that's often lurking in building water systems. Hotels, office buildings, fountains and hot tubs can be the source for this sometimes fatal infection. About the disease Legionnaires is caused by bacteria called Legionella, which is found naturally in freshwater environments, like lakes and streams, according to the Centers for Disease Control and Prevention (CDC). Outdoors, it rarely causes infections. But it can become a problem when it grows indoors and multiplies easily in water systems like air conditioners, hot tubs, plumbing, fountains and even water mist sprayers in the produce departments of grocery stores. Most Legionnaires outbreaks have happened in large buildings, maybe because their complex plumbing systems allow the bacteria to grow and spread easily, points out the Mayo Clinic. Because home and car air-conditioning units don't use water to cool the air, they're not at risk. The disease was named after an outbreak in Philadelphia in 1976, where many people who went to an American Legion convention got sick with a lung infection. How the infection spreads Most people get infected when they inhale tiny water droplets containing Legionella bacteria. This might be from water running through a ventilation system in a building or from the spray from a shower, faucet, fountain or hot tub. It's unusual, but people can also get sick by aspirating drinking water containing the bacteria. That's when water accidentally gets into the lungs as you drink. People don't usually spread Legionnaires' disease to others, although it's possibly under very rare circumstances, according to the CDC. Most healthy people exposed to the bacteria do not get sick. If the bacteria causes a mild infection, it's known as Pontiac fever. People most at risk of Legionnaires' disease are those 50 and older, current or former smokers, and people who have chronic lung disease, weakened immune systems, cancer or other underlying illnesses. Symptoms and treatment Like other types of pneumonia, Legionnaires' symptoms include: CoughShortness of breathFeverMuscle achesHeadachesWeakness and fatigue Chest X-rays should show evidence of the bacteria, according to the CDC. Legionnaires' disease is treated with antibiotics. The more quickly treatment begins, the more likely there won't be any complications. According to the CDC, about one in 10 people who get Legionnaires' disease will die.