Legionella is a gram-negative aerobic bacterium that is present in aquatic environments. The best conditions for its proliferation are stagnation conditions, the presence of biofilm, the presence of amoeba and the presence of sediments or incrustations. It also survives with water temperatures between 5.5°C and 55°C, although the most favourable conditions for development are temperatures between 25°C and 42°C.
It also has a good ability to survive pH conditions that can vary from 5.5 to 8.1, i. e. both in acidic and basic environments.
Particular dangerousness comes from the micro-absorption of aerosol in which the bacterium can be contained, which can lead to legionellosis, severe form of highly lethal pneumonia.
. The aerosol can be generated in various situations including opening a faucet, showering, draining toilets, cooling towers, etc.