A gram negative bacillus that is widely distributed in warm, wet environments and is of particular concern in air-conditioning cooling towers and hot water systems.

Disease

• Legionella pneumophilia is the main cause of legionellosis or Legionnaire's disease
• other species may also cause disease particularly in immunocompromised patients

Mode of transmission

Legionellosis can be acquired by:

• the inhalation of aeosols containing Legionella
• by aspiration of water or respiratory secretions containing Legionella
• by direct instillation during respiratory tract manipulation

Significance in endoscopy

Pseudoepidemics have occured where L. pneumophilia has been found in broncheoalveolar lavage specimens due to contaminated water used to rinse disinfected bronchoscopes, either because of use of tap water for the final rinsing or because of inadequate maintenance of water filters.
source : http://www.health.qld.gov.au/EndoscopeReprocessing/module_1/1_3d.asp#Cdiff