Safe working methods needed to protect against Legionella

September 23/2020

The Finnish Food Authority and the Finnish Institute for Health and Welfare (THL) found Legionella bacteria in a variety of growing media, compost and digestate samples. Illness caused by Legionella can be prevented by raising awareness of the Legionella risk and advising consumers and manufacturers on safe working methods.

The Finnish Food Authority and THL investigated the prevalence of Legionella bacteria especially in fertilising products whose raw materials are subject to an increased Legionella risk due to their origin or treatment. Samples were taken, for example, from bagged potting soil, bulk garden soil, composts, and digestate from biogas plants used as arable crop fertiliser. The project also examined, separately, the effects of different raw materials, manufacturing processes, hygienisation and product preservation on the prevalence and concentration of Legionella bacteria.

Legionella bacteria are common in soil and water systems and can increase significantly in concentration under suitable environmental conditions. They reproduce in humid and warm conditions and can therefore be present in harmful concentrations for example in water systems, soil and composts.

Legionella were found in almost all samples

Legionella bacteria were found very often in the samples studied and also in high concentrations in some samples, determined both by using culture techniques and by a gene amplification method (qPCR). Based on the project results, although Legionella were found in almost all the samples examined, the choice of raw materials and processing methods affected the Legionella levels of fertilising products. Results also showed that Legionella was not destroyed during the fertiliser production process.

‘The safe level of Legionella in the products investigated is not yet known, but neither is the infective dose of Legionella causing legionellosis. At this stage, where attempts to decrease the levels of Legionella to a non-harmful level have not yet succeeded, raising awareness of the Legionella risk and advising consumers and manufacturers on safe working methods is probably the best way to prevent illness,’ says Jaana Kusnetsov, a senior researcher at THL.

Legionella also cause a variety of infections, even in normally healthy persons

Legionella bacteria can cause infection, i.e. legionellosis, if they enter the body via inhaling aqueous aerosols or dust particles containing the bacteria. In addition to severe pneumonia, legionellosis can also cause skin, circulatory system and intestinal infections. It is therefore important to identify the risk of illness caused by Legionella and to protect against it. People belonging to vulnerable groups have an increased risk of illness caused by Legionella, but the bacteria can also infect even healthy persons.

The number of cases of legionellosis has increased significantly in Europe. Usually, cases of legionellosis in Finland have been related to water, but in recent years some cases relating to growing media and organic soil improvers have also been reported. The circular economy has increased the use of organic materials generated in different production processes, such as the use of municipal and industrial waste water in the manufacture of fertilising products.

There has been no research in Finland on the preservation of Legionella in the processed raw materials or on the possibility of Legionella ending up in marketed fertiliser products.

Welcome to the remote research seminar on 29 September from 3:00 to 4:00 pm

Welcome to learn more about the topic at the Finnish Food Authority’s research seminar on 29 September from 3:00 to 4:00 pm (in Finnish) (Skype link for registered participants). 



Read more: 

Safe working methods to protect against Legionella for people handling soil improvers and growing media  (pdf, in Finnish)

Scientific project: The occurrence of Legionella bacteria in circular economy products
Research projects’ final reports:

Additional information:

Liisa Maunuksela, PhD, Research Director, Finnish Food Authority, tel. +358 (0)400 256 097
Jaana Kusnetsov, PhD, Senior Researcher, National Institute for Health and Welfare, tel. +358 (0)29 524 6347