Tutorial Legionella. What do the legionella, where to find them. Which associations and authorities deal with it, which rules are set up. What can be done against Legionella and how can success be checked. Aerosols and dust as the source of infection with Legionella. It has taken many years, until people have noticed, that water does not exist solely in liquid and solid form. The idea, that water dissolved in air is present in the environment, brings many people already to the edge of imagination. Where to find aerosols, there is also found legionella. Few of these species in biologically film are dangerous to humans. However, a risk arises from the increase under favorable conditions up to a number, which weakened humans can not fend off with the natural systems.