Legionella is a commonly occurring bacteria found in both natural and artificial water systems. In Legionnaires’ disease, a serious and potentially fatal form of pneumonia, the infection is caused by inhaling contaminated water droplets containing Legionella bacteria.
Legionella bacteria are commonly categorised into two groups, which are Legionella pneumophila and Legionella species. Legionella pneumophila can be further divided into Legionella pneumophila serogroup 1 and Legionella pneumophila serogroups 2-15. There are over 50 species of Legionella identified by the World Health Organisation (WHO) and a large proportion of these have been clinically identified as human pathogens.