Legionella are aerobic, non-spore forming, typically flagellated, gram-negative bacteria. The genus was named after a severe epidemic of pneumonia at an American Legion convention in 1976, which led to the isolation and characterization of L. pneumophila. Since then, thirty (30) species of the genus Legionella have been identified.

In humans, L. pneumophila can cause Legionnaires’ diseases and Pontiac Fever.
Legionnaires’ disease is manifested by severe pneumonia, gastrointestinal symptoms and, in some cases, death. Pontiac fever is a non fatal, non pneumonic, influenza- like syndrome typified by headache, fever, and myalgia. Legionella bacterial occur naturally in aquatic habitats.