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   Legionella pneumophila
About the Project
Home > Education > Contaminants & Risks > ​Drinking Water Contaminants > Legionella​​
Quick Facts
  • Contaminant Type: Bacteria
  • Health Effects: Pontiac fever (flu-like disease) & Legionnaires’ disease (severe pneumonia)
  • Found in: man-made systems like cooling towers, water misters, decorative fountains, hot tubs, and showers
  • Treatment Options: Point-of-use treatment such as Ultraviolet (UV) disinfection and filters rated for removal of bacteria 
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Image Credit: PWGC
About Legionella
Legionellosis is a respiratory disease caused by Legionella bacterium. The infection presents in two forms: Pontiac fever is a mild to moderate flu-like illness, which can advance to the more severe Legionnaires’ disease, a form of pneumonia.

Legionella was first discovered in 1976 when a mysterious illness struck staff and attendees at a convention for the American Legion in Philadelphia, PA. During this outbreak, 182 people were sickened and 29 died. Additional illnesses were eventually linked to cooling towers, water misters, decorative fountains, hot tubs, and showers. From these sources, the bacteria could be aerosolized and spread in micro-droplets of water that were inhaled by unsuspecting victims. Most cases today occur in middle-aged men and show a seasonal increase in summer to fall months, particularly in the eastern US, but women and older populations are also at risk; outbreaks do occur year-round.
Legionella Outbreaks
  • The CDC has been monitoring the causes of water-associated outbreaks since 1971 to 2014. 
  • Over time, Legionella has emerged as a primary cause of waterborne disease.
  • Despite extensive regulation and monitoring of drinking water over time, microbial and chemical outbreaks continue to occur.
Full infographic available:
major_causes_of_outbreaks.pdf
File Size: 461 kb
File Type: pdf
Download File

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Major causes of drinking water-associated outbreaks (2013-2014)
Who is most at risk?
  • Elderly
  • Dialysis Patients
  • Diabetics
  • Smokers
  • Immunocompromised
Treatment
While many outbreaks are associated with larger buildings and healthcare facilities, cases associated with smaller businesses and homes are likely to go undetected. Point-of-use (POU) treatment techniques such as Ultraviolet (UV) disinfection and filters rated for removal of bacteria are effective barriers and recommended to minimize at-risk population exposures to Legionella from faucets and showerheads.
Related Articles
  • 04/2013 Evidence of Drug-Resistant Bacteria in Water [Link]
  • 12/2013 Deadly Legionella: Commonly Found in US Water Systems [Link]
  • 06/2015 POU Prevention of Healthcare-acquired Waterborne Infections [Link] 
  • 07/2016 The Rise of Legionella [Link]
  • ​01/2017 POU Filtration: A Water Safety Plan Essential [Link]
  • 07/2017 Effective Immediately: Healthcare Facilities Required to Reduce Legionellosis Risks from Tap Water [Link]
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WQRF | Knowledge of Quality Water


  • Home
    • WQRF Board
  • Network
    • Water Experts
  • 2025 Student Poster Gallery
  • RESEARCH
    • Research & Summaries
    • Webinars
    • Request for Proposals
  • Data Tools
    • Contaminant Map
    • 1-Minute Video Summaries
    • Softening Benefits Calculator
    • Softened Water Toolkit
  • EDUCATION
    • PFAS Resources
    • Contaminants & Risks
    • Treatment Options
  • Next Wave Campaign
    • Campaign Leadership
    • Campaign Supporters
  • Donate
  • Events
    • Walk for Water
    • WQRF @ WQA Convention