Legionnaires’ from Compost

Recent press reports suggest links between bagged compost and legionnaires’ disease, as calls are made for better warning labels.

Taking potting compost from the bag

Taking potting compost from the bag

An article in the current issue of Eurosurveillance points to three cases of Legionnaires’ disease in Scotland between 2008-2009, caused by a particular strain, Legionella longbeachae Sg 1 associated with bagged potting compost.

Legionnaires’ Disease is a water born bacteria which causes a type of Pneumonia and is acquired by droplet inhalation.  It is thought to affect men more than women, especially the middle aged and elderly.  Those with existing medical conditions of the respiratory or immune system are also at greater risk.

Until recently, an association between cases of Legionnaires’ disease and gardening or use of potting mixes, was thought to be limited to Australia and New Zealand.  However, is has now been identified in Japan, the United States, the Netherlands and Switzerland.

In the UK, only nine cases of L. longbeachae have been reported since 1984. Five of them, including the three cases in Scotland have been linked to the use of potting composts.

Although the report does highlight a potential risk to gardeners from bagged potting compost, it also makes it quite clear that two of the people concerned in the Scottish outbreak had other health factors which put them “at risk” from infectious diseases.

Compost can be in plastic bags for quite some time and water contained in the compost is just sitting in a damp, often warm environment which is an ideal breeding ground for many bacteria including Legionella.
  • Always check the date on a bag of compost.
  • A bag of compost should have a sweet, earthy odor. If it smells sour, it has been in the bag too long and is decaying. It should be spread on the garden and dried until the sour smell goes away.  It should not be used for seed sowing or potting.
  • Empty compost out of a bag gently so as not to cause dust particles and do not lean over the bag with your face when decanting the compost.

Standing water is a health risk

  • Gardener’s should be aware that any container which has held or does contain water, especially spray bottles, could cause risk of legionnaires’ and other disease.
  • Always clean spray guns, bottles and pumps thoroughly before use and empty and air dry well, before putting away for the winter.
  • Never leave containers sitting full of water for long periods of time.
  • Water butts should be treated with proprietary products and it is best to avoid contact with any water that has stood for long periods.  Use the tap on the water butt to dispense water into your can.  Use domestic tap water to fill spray bottles and in the greenhouse.

Wear gloves and wash your hands.

Apart from the damage that soil does to your hands, it can contain all sorts of nasties.

One of the easiest way to avoid picking these up on your hands is to wear gloves and always wash and scrub your hands well after gardening.

Make your own compost.

Making your own compost usually involves the rotting material reaching very high temperatures as the materials break down.

A lot of bacteria cannot survive these temperatures and are destroyed during the composting process.

Air circulates through the compost heap and the resulting compost does not sit in warm, damp plastic bags.

More information

Eurosurveillance, Volume 15, Issue 8, 25 February 2010  – Legionella, springtime and potting soils

BBC News article – Compost link to Scottish Legionnaire’s cases

HSE information – Causes and symptoms of Legionnaires’ Disease.

Health Protection Scotland – Article about the Scottish compost linked Legionnaires’ cases.

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