Legionella bacteria can pose a serious health risk in the indoor environment. Legionella is a gram-stain negative bacteria that was discovered in 1976 after an outbreak in Philadelphia. The outbreak occurred at an hotel during a convention for the American Legion, where 34 died and hundreds were hospitalized. Up to that point in time, the bacteria had not been discovered or named.
Legionella can be found naturally in freshwater environments as well as in man made water systems such as cooling towers, water tanks, and decorative fountains. It typically forms in warm, stagnant water and spreads when that water becomes aerosolized. It can form two different types of infections in humans:the more severe Legionnaires’ disease and the milder Pontiac fever.
Legionnaires’ disease is a type of pneumonia, which is typically more fatal than a common pneumonia. Exposure occurs when Legionella contaminated water is aerosolized and then inhaled by a person. Symptoms of Legionnaires’ disease include cough, high fever, shortness of breath and wide variety of symptoms similar to pneumonia. The infection is typically treated with antibiotics. The people who are most at risk for Legionnaires’ disease are smokers, elderly and the immunocompromised.
Another infection caused by the Legionella bacterium is Pontiac Fever. Pontiac Fever is a condition that resembles influenza, and is a Legionella infection that does not include a form of pneumonia. It was discovered retrospectively after the Legionnaire’s disease outbreak of 1976 when blood samples from a 1968 influenza outbreak in Pontiac, Michigan showed the presence of the Legionella bacterium. Pontiac Fever is treated with antibiotics like Legionnaires’ disease. Both Legionnaires’ Disease and Pontiac Fever are generally not spread from person to person.