Safe working methods needed to protect against Legionella

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, said a press release issued recently by the Finnish Food Authority.

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 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,’ said Jaana Kusnetsov, a senior researcher at THL.

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 Finnish Food Authority’s research seminar on the topic will be held remotely on 29 September from 3:00 pm to 4:00 pm.