Legionella bacteria were discovered following a pneumonia outbreak at the 1976 American Legion Convention in Philadelphia (Brenner 1987). The bacteria isolated from infected lung tissue and identified as the causative agent of this pneumonia outbreak was named Legionella pneumophila, receiving the name Legionella to honor the stricken American legionnaires and pneumophila from the Greek word meaning “lung-loving” (Fang et al. 1989).

Legionella are considered to be ubiquitous in the aquatic environment, including both natural water bodies and man-made waters (EPA 1985) and can survive in temperatures from 0-60°C. Research has revealed that Legionella thrive in biofilms, and interaction with other organisms in biofilms is important for their survival and proliferation in water.

Human exposure to Legionella-contaminated sources can result in outbreaks of legionellosis. Legionellosis outbreaks have been attributed most frequently to exposure to contaminated potable water, cooling towers, or components of water distribution systems. Outbreaks of legionellosis are typically categorized as nosocomial (i.e., hospital-acquired), travel-acquired, or community-acquired. Nosocomial outbreaks have been linked to hospital potable water supplies as well as cooling towers (EPA 1998).

In June 2017, Centers for Medicare and Medicaid Services released a revised memorandum for the requirement to reduce Legionella risk in healthcare facility water systems to prevent cases and outbreaks of Legionaires disease. BAL services many facilities in their routine monitoring in both Rhode Island and Massachusetts.