Legionella pneumophila

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Human and animal.

Infection normally occurs after inhaling an aerosol (fine airborne particles) containing Legionella bacteria. [1]
Anywhere from 8,000 to 18,000 people are hospitalized each year in the U.S. with Legionnaires' disease. (EH&E) Between 1980 and 1998, 35% of Legionnaires Disease cases met definition of nosocomial infection.[2]
Disease is usually associated with man-made environments, such as cooling towers, whirlpools, and building water systems, where warm water (25C–42C) and biofilms support growth and survival of Legionella species. [3]

During an outbreak in the Netherlands the incubation period was reported to be 2-19 days (median 7 days, n=136), 16% of these individuals showed incubation times exceeding 10 days. [4]

Legionnaires disease has a 25% mortality rate. (Medscape)
Legionnaires' disease can be very serious and can cause death in up to 5% to 30% of cases. [5]
Between 1980 and 1998, the case fatality ratio decreased from 34% to 12% (P<0.001) for all cases, 46% to 14% (P<0.0001) for nosocomial cases, and 26% to 10% (p=0.05) for community-acquired cases. [2]

U.S. legionellosis cases reported annually increased 217%, from 1,110 in 2000 to 3,522 in 2009, and the crude national incidence rate increased 192%, from 0.39 per 100,000 persons in 2000 to 1.15 in 2009. [6]
Between 1980 and 1998, the median annual number of cases was 360 cases/year. [2]
Elderly individuals, smokers, and people with underlying respiratory or immunocompromising conditions are at increased risk for Legionnaires disease. [7]

Benin figure.png
Figure 1. No. of cases of legionnaires disease (LD) and rate per 100,000 US residents, by age group, 1980–1998.[2] (Surveillance data collected by the Center for Disease Control as presented in Benin, Andrea L, Robert F Benson, and Richard E Besser. “Trends in Legionnaires Disease, 1980–1998: Declining Mortality and New Patterns of Diagnosis.”)

Duration of infectiousness and disease


Symptoms include a high fever, chills, cough, muscle or headaches. These symptoms are common to most forms of pneumonia so diagnosis relies on chest X-rays and tests performed on sputum, blood, and urine. [5]


Asymptomatic Rates

Excretion Rates (see Exposure)


A thin, aerobic, pleomorphic, flagellated, non-spore forming, Gram-negative bacterium of the genus Legionella.[8] [9]
Legionella species are weakly gram-negative bacteria found primarily around fresh water environments, such as lakes and streams, where the bacteria use free-living amoeba as hosts for intracellular survival and multiplication.[3]


  1. Health Protection Agency. “Modes of Infection: Aerosolisation.” Web. 21 May 2012. http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1204186178183?p=1191942128209
  2. 2.0 2.1 2.2 2.3 Benin, Andrea L, Robert F Benson, and Richard E Besser. “Trends in Legionnaires Disease, 1980–1998: Declining Mortality and New Patterns of Diagnosis.” Clinical Infectious Diseases 35.9 (2002): 1039–1046. Web. 21 May 2012. Cite error: Invalid <ref> tag; name "benin" defined multiple times with different content
  3. 3.0 3.1 Fields BS, Benson RF, Besser RE. Legionella and legionnaires’ disease: 25 years of investigation. Clin Microbiol Rev 2002; 15:506–26.
  4. Den Boer, Jeroen W. “A Large Outbreak of Legionnaires’ Disease at a Flower Show, the Netherlands, 1999.” Emerging Infectious Diseases 8.1 (2002): 37–43. Web. 9 May 2012.
  5. 5.0 5.1 Center for Disease Control. "Patient Facts: Learn More about Legionnaires' disease". http://www.cdc.gov/legionella/patient_facts.htm Cite error: Invalid <ref> tag; name "CDC" defined multiple times with different content
  6. Center for Disease Control. "Morbidity and Mortality Weekly Report: Legionellosis". http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6032a3.htm
  7. Marston BJ, Lipman HB, Breiman RF. Surveillance for legionnaires’ disease: risk factors for morbidity and mortality. Arch Intern Med 1994; 154:2417–22.
  8. Madigan M; Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1.
  9. Heuner K; Swanson M (editors). (2008). Legionella: Molecular Microbiology. Caister Academic Press. ISBN 978-1-904455-26-4.

CDC Patient Facts