Finland recorded more than 80 cases of legionella pneumonia in 2025, the highest annual total on record, with authorities linking many infections to contact with soil and compost products.

Health officials said about half of those infected reported handling soil before falling ill, including changing potting soil or emptying compost.

The Finnish Institute for Health and Welfare and the Finnish Food Authority issued a warning on risks tied to dry soil and compost products after the rise in cases.

Previous annual figures stood at about 50 cases in each of the two years before 2025.

Officials said the increase follows a wider pattern across Nordic countries, with Sweden reporting similar trends. The cause behind the rise in soil-related infections remains unclear.

Riikka Ruotsalainen, a specialist at the Finnish Institute for Health and Welfare, said in a statement that “part of the increase in infections may be explained by more active testing of the disease”.

Legionella bacteria occur in small amounts in fresh water and soil. They also appear in compost and growing media used in homes and gardens. Infection occurs when bacteria enter the lungs, where they cause pneumonia. In some cases, bacteria enter the body through cuts in the skin.

The agencies advised people to open soil bags away from the face and to use low water pressure when dampening materials, to use gloves when handling soil and to wash hands after contact. People with cuts or broken skin should cover affected areas before exposure.

Respiratory masks rated FFP2 or FFP3 offer protection in situations where dust cannot be avoided. Officials also advised storing soil products away from direct sunlight, as higher temperatures inside bags support bacterial growth.

The risk of illness remains highest among older people and those with weakened immune systems. Smoking and lung disease also increase the risk. Most healthy individuals do not develop illness after exposure.

Legionella infections in Finland have traditionally been linked to water systems. The bacteria grow in temperatures between 20 and 45 degrees Celsius and appear in showers, hot tubs, humidifiers and cooling systems.

HT