Legionella bacteria can be found in the biological wastewater treatment plants of the forest industry. Legionella is not a forest industry specific issue, but its occurrence in other industrial branches has not been examined as reliably.
Personnel working or visiting in biological wastewater treatment facilities are required to wear respiratory protective equipment which prevent exposure to the bacteria.
Employee exposure study completed in 2007
The study, which was completed in the end of 2007, examined pulp and paper mill employee exposure to environmental bacteria that cause infections via the respiratory ducts. The study was conducted at 21 wastewater treatment facilities and 292 employees were included in it.
The results indicated that:
o Persons working in wastewater treatment plants had been exposed to Legionella bacteria as elevated levels of Legionella antibodies were discovered in their blood tests. However, increased occurrence of respiratory infections or any other clear effects were not detected.
o Atmospheric samples demonstrated that aerosols, which contain viable and cultivable Legionella bacteria and mycobacteria, were formed during ordinary use of aerating basins.
o Employees should at all times wear respiratory protective equipment at the wastewater treatment facilities of the forest industry.
o Exposure levels in the plants and vicinity of treatment areas should be examined further.
Studies have been continued
Examinations of wastewater treatment facilities in the Finnish forest industry commenced in June 2005. After finding legionella bacteria the employees working at the biological wastewater treatment plants were immediately instructed to wear respiratory protective equipment which prevent exposure.
Studies have continued. In 2010, a research project was carried out in cooperation with the Finnish Institute of Occupational Health. In the project a guide was developed for the assessment and control of microbiological risks in the working environment in the pulp and paper industry.
The search for Legionella was triggered by Swedish reports of substantial Legionella concentrations in the aeration basins of biological wastewater treatment plants in spring 2005. One employee of a Swedish paper mill was suspected of having contracted Legionella-based pneumonia, legionellosis, from bacteria in an aeration basin in November 2004.