Legionella pneumophila: More than just a Legionnaire’s Disease

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Legionella pneumophila was the culprit behind the death of 23 people in Toronto in 2005 and 13 in Quebec City in 2012. This clever little organism can cause legionellosis, which is 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’ Disease 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.

Legionella pneumophila 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

Legionella and other bacteria colonies

Legionella and other bacteria colonies

The presence of Legionella in a water source is verified by taking test 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) or Polymerase Chain Reaction (PCR).

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 us at 905-290-9101.


  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.

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Dr Jackson Kung'u
Dr. Jackson Kung’u is a Microbiologist who has specialized in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analyzed thousands of mould samples from across Canada. He also regularly teaches a course on how to recognize mould, perform effective sampling and interpret laboratory results. Jackson provides how-to advice on mould and bacteria issues. Get more information about indoor mould and bacteria at www.drjacksonkungu.com.
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