Legionella bacteria infecting people also commonly found in organic soil improvement agents and growing media

April 10/2019

The Finnish Food Authority and the National Institute for Health and Welfare have been studying the occurrence of Legionella bacteria in organic soil improvers and growing media. More than 90 per cent of the samples studied contained Legionella, some of them in great numbers. The results of the study support the view that Legionella bacteria are commonly found in soil and in different organic fertilizer products. The research project has already examined the impact of different manufacturing processes on the occurrence of Legionella bacteria. In 2019, the focus of research will be on how storage conditions of the aforementioned products affect the bacteria.

Legionella bacteria may cause an infection, legionellosis, that is dangerous to humans. The factors that increase the risk of disease include advanced age, smoking and different illnesses that lower resistance. Basically healthy people may also become ill. Usually, people get infected by inhaling water aerosols or dust particles containing Legionella bacteria, and sometimes through broken skin. In the most serious cases, when the bacteria reach the lungs, Legionella may cause pneumonia with an average mortality rate of 8 - 10 per cent. In addition to respiratory infections, it may also cause skin, heart and intestinal infections.

The number of legionellosis cases has increased in Europe over the last few years. In Finland, as yet, only a few cases of legionellosis caught from organic fertilizer products have been reported, but it is possible that more cases will occur, particularly if protective measures are not improved.

“Legionlla bacteria are relatively common environmental microbes, but most people exposed to them do not become ill. The incubation period from infection to first symptoms varies from 2 to 10 days. In case of pneumonia, healing from Legionella pneumonia requires treatment with the right type of antibiotics, even intensive care. It is important to identify the risk caused by Legionella, protect oneself against the bacteria and diagnose the disease,” says PhD Jaana Kusnetsov, Senior Researcher from the National Institute for Health and Welfare.

Legionellosis infection is always of environmental origin

In small concentrations, Legionella is commonly found in water and soil, but the concentrations may grow significantly as a result of human activity. Legionella is generally detected in different water systems.

 “The risks of infection must be taken into account in the occupational health and safety instructions for employees handling organic fertilizer products. Furthermore, users, such as farmers and people working in their own gardens, should be aware of the risks and take sufficient precautions, if necessary,” says PhD Liisa Maunuksela, Research Director at Finnish Food Authority.

When handling organic fertilizer products, such as growing media and soil improvers, the following instructions should be followed, as appropriate:

  • Avoid exposure to dusty material, if necessary, moisten them with caution, using low water pressure. Do not use a pressure washer to moisten soil or compost materials. 
  • If you cannot avoid dust from flying in the air, you should wear a protection class FFP3 respirator mask.
  • Protect any wounds or broken skin on your hands. Wear protective gloves and wash your hands carefully afterwards. If your hands are dirty, do not take them near your mouth or nose.
  • Store bags of growing media away from direct sunlight. At 20 - 40° C, the inside temperature of a bag held in sunlight is ideal for the growth of Legionella bacteria. When opening a bag of soil, keep the open end turned away from your face.
  • Remember hand hygiene and sufficient protection when handling and spreading growing media for lawn as well.

The concentrations of Legionella bacteria are studied in different soil improvement and growing media products using cultivation and PCR methods.

Sampling and analyses will be continued throughout 2019. The research project will end in 2020.

Read more about the research projects
The occurrence of Legionella bacteria in recycled products, the Government's key project
Legionella in growing media

Further information:
Research Director Liisa Maunuksela, Finnish Food Authority
+358 400 256 097
Senior Researcher Jaana Kusnetsov, National Institute for Health and Welfare
+358 29 524 6347