Legionella pneumophila: More than just a Legionnaire's Disease

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Legionella pneumophila was the culprit behind a recent health threat in Toronto. This clever little organism can cause legionellosis, which is more commonly referred to as Legionnaires’ Disease.

Legionnaires’ Disease is primarily a disease of the lungs, and although the bacteria is generally thought of as an opportunistic pathogen, it can be a serious threat to health, causing death in 5-30% of those infected(1).


Legionnaires’ in the News

The disease got its name from where it was first discovered: it had infected a group of people at a Legion Convention, where Legionella had contaminated the cooling towers of the air conditioning system. The system caused some of the water to be aerosolized and circulated in the building, where droplets containing the organism were inhaled by guests(2).

A more recent outbreak occurred in a Toronto-based long-term care home in September 2005. The source of contamination was identified as the air conditioning cooling tower on the roof of the building.


Who is at Risk?

The disease itself begins in the lungs, which is the entry point for the organism. It is for this reason that people with compromised defenses are at greater risk of developing Legionnaires’ disease: the immunocompromised, the elderly, or heavy smokers and those with lung disease.


What are the Symptoms?

The symptoms of Legionnaire's Disease are often flu-like: fever, chills, cough, muscle aches, headache, tiredness, loss of appetite, and possibly diarrhea. The patient will generally also have pneumonia, and their kidneys may lose some function(1). Within the lungs, the bacteria infect white blood cells, breaking them apart and causing fluid to accumulate.
The bacteria can incubate in the host for 2-10 days before any symptoms become evident.
Legionella pneumophila has a cousin, Legionella micdadei, that causes Pontiac Disease, a milder illness which is more flu-like(2).


Where is Legionella found?

Legionella is a waterborne bacterium that prefers higher temperatures (30-40° Celsius) but have been found in environments of anywhere from 0-63° Celsius.


Infection and Treatment

The bacterium cannot be transmitted from person to person. It is generally believed that the main mode of infection is by aerosolization of water droplets containing the organism, but recently another theory has been put forth that drinking contaminated water may allow entry of the organism if a person chokes on the water and allows some of the liquid to proceed down the windpipe instead of the esophagus. Legionella infection is treated with antibiotics.


Testing and Decontamination

The presence of Legionella in a water source is tested for by taking water samples from the suspect source(s) (cooling towers, humidifiers, whirlpool spas, water heaters, etc.) and analyzing in the laboratory. This can involve the use of differential media (such as Buffered Charcoal Yeast Extract Agar) or molecular techniques like Enzyme Linked Immunological Assay (ELISA).

If it is determined that Legionella is indeed present, there are a few options for treating the system. Super-chlorination or super-heating may be used. The former refers to introducing chlorine gas into the system and allowing it to work for a few hours, and the latter involves running very hot water (around 70° Celsius or higher) through the system for an adequate timeframe based on each system(4).


For more information on testing for Legionella, please contact Meagan Klub at 905-290-9101, extension 112.


References

1. Centres for Disease Control. 2002. Legionellosis: Legionnaire's Disease (LD) and Pontiac Fever. Atlanta, USA. Online. http://www.cdc.gov/ncidod/dbmd/diseaseinfo/legionellosis_t.htm
2. Salyers A, Whitt D. 2002. Bacterial Pathogenesis: A Molecular Approach. ASM Press, Washington, USA. 311-21.
3. Steinert M, Hentschel U, Hacker J. 2002. Legionella pneumophila: an aquatic microbe goes astray. FEMS Microbiology Reviews. 26:149-62.
4. Yang, Chin S. Sampling and Controlling Legionella Bacteria in Domestic Water Systems. Online.
   http://www.stl-inc.com/technical_Papers/Sampling&Controling%20Legionella%20Bacteria in%20Domestic%20water.pdf

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About the Author

Meagan Klub is a Microbiologist with a particular interest in pathogenic bacteria (disease-causing bacteria). She graduated from the University of Guelph in Guelph, Ontario, Canada with a Bachelor's degree in Microbiology.

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