Health Stream Article - Issue 56 - December 2009

Industrial Exposures To Legionella

Health agencies in the UK recently identified two cases of Legionella pneumonia linked to workplace exposures to water aerosols. These cases once again highlight the potential health risks of Legionella growth in warm water sources coupled with the use of spray-generating devices. The investigation was triggered when two middle aged men were admitted to the same West Midlands hospital with legionellosis on the same day in May 2008. Both men worked at a factory which manufactured construction and agricultural equipment, but they had no other apparent common exposures to aerosolised water sources. Potential sources of aerosol exposure assessed at the workplace included the hot and cold water supplies to restrooms and changing rooms, a paint mist trap using ambient temperature water, and a degreasing/rinsing tunnel using water-based solutions (at 55-60 degrees C or 25-38 degrees C) to clean metal parts before painting. Water tests revealed Legionella pneumophila serogroup 1 in samples from the degreasing/rinsing tunnel at levels above 30,000 colony-forming units per litre. There was no aerosol extraction system on the tunnel and brushes covering the conveying railings (which would have reduced spray emissions from the tunnel) were missing. One of the infected workers worked in the section of the factory containing the degreasing/rinsing tunnel while the other walked past this equipment several times a day. After initial cleaning and shock disinfection of the water tanks supplying the degreasing/rinsing tunnels, a biocide dosing regime was established to combat Legionella growth. Procedures were also introduced to drain and clean the tanks every weekend when the plant closed.

Eleven other workers at the plant who had been absent from work due to respiratory illness at some time during the previous four weeks were tested for urinary Legionella antigen, but none were positive. The investigators note that aqueous cleaning systems are replacing solvent-based cleaning systems for metal degreasing because of health concerns over solvent exposures for workers. However these aqueous systems may generate unforseen health risks due to the combination of warm water temperatures, nutrients from washing metal parts, recirculation of water, and convoluted surfaces which favour biofilm growth. If aerosols are allowed to escape from the equipment, workers may be at risk of infection. Five similar aqueous cleaning systems were subsequently tested by the UK Health and Safety Executive and Legionella bacteria were detected in four systems, suggesting that contamination is common. This has led to the recommendation that these systems need to be included in Legionella risk assessment and management plans for workplaces.

Legionnaires' disease cluster linked to a metal product aqueous pre-treatment process, Staffordshire, England, May 2008. Coetzee N et al. Euro Surveill. 2009;14(40).

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