Compost as a source of the deadly Legionella bacteria

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Legionella Colonies

Legionella bacteria

Compost may contain the potentially deadly Legionella bacteria.

In fact, cases of legionellosis caused by Legionella bacteria in compost have been on the increase worldwide. In October 2013, a case of legionellosis linked to compost exposure was reported in Richmond, British Columbia.

Legionellosis is a term used for any disease, caused by Legionella.

Two forms of legionellosis are common. A mild form known as Pontiac Fever and a more severe form of pneumonia known as Legionnaires’ Disease. The association between commercial compost and legionellosis was established in Australia in 1989.

Since then, Legionella longbeachae, the cause of Legionnaires’ disease associated with compost, has been isolated from fresh potting media. Legionella longbeachae is less common in Canada than Legionella pneumophila.

Unlike other Legionella bacteria, Legionella longbeachae is not found in water. It causes legionellosis symptoms ranging from mild flu-like illness to severe pneumonia and death.

Legionella pneumophila is the species responsible for the first documented outbreak of Legionnaires’ disease in 1976. It is the cause of the majority of legionellosis cases in the world and it’s commonly found in water.

Exposure to Legionella bacteria

The Legionella bacteria are not transmissible from person to person. How Legionella longbeachae are spread is not well known. It is speculated that the bacteria is inhaled in or spread from hands contaminated by handling potting mix to mouth. Exposure to Legionella pneumophila is primarily airborne through aerosolized water containing the bacteria. Legionella containing aerosols can be produced by:

  • showers;
  • cooling towers;
  • air conditioning systems cooled by water;
  • humidifiers;
  • whirlpool spas.

Compost as a source of Legionella bacteria

Studies have demonstrated the diversity of Legionella species found in commercial composts and potting soils. The most commonly isolated non-pneumophila Legionella species from compost are Legionella longbeachae, Legionella bozemanae, Legionella micdadei, Legionella dumoffii and Legionella feeleii. Others include Legionella bozemanii, Legionella sainthelensi, and Legionella micdadei.

While cases of legionellosis associated with compost are uncommon in North America, they are quite common in UK and across Europe , Australia and New Zealand.

Our team here at Mold & Bacteria Consulting Laboratories offer a comprehensive bacteria screening and analysis (including Legionella). You can contact us by email or telephone to discuss your case further.

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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
Dr Jackson Kung'u

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