Legionella was the bacterium identified many years ago as the cause of an outbreak of serious pneumonia, sometimes fatal, in a group of American Legion attendees at a 1976 convention in Philadelphia. About 30 of the 180 cases died.
Here’s a story about another outbreak attributable to contaminated air conditioning systems. Legionella, a gram negative culprit bacterium is inclined to inhabit the water in air conditioning systems and moist places, kinda like a fungus. Produces a flu like syndrome, with some intestinal symptoms as a part of the complex. More lethal in the old and in patients with underlying pulmonary disease.