Legionella, springtime and potting soils.

Legionnaires’ disease has been named after the outbreak in Philadelphia 1976 when a mysterious pneumonia affected a large number of members of the American Legion, a United States military veterans association, which held a gathering at a hotel [1]. Legionella, the bacterium causing the disease was identified several months after this outbreak for the first time. Today we know that there are about 50 different species of Legionella and that not all of them seem to be pathogenic to humans. The vast majority of reported cases are infected with L. pneumophila by inhalation of aerosols (water droplets) containing the bacteria, which is the route of infection for most Legionella cases. This is also described in an article by Joseph and Ricketts in this issue [2].