Excellent article by an ex Health and Safety Executive specialist inspector
10 things you should know about Legionnaires' Disease and its prevention
1. The disease was first recognised following an outbreak in Philadelphia in 1976 and named after the veterans’ organisation, the American Legion, who were holding a convention and whose members were the main victims.
2. Legionnaires’ Disease is a form of pneumonia and is fatal in about 12% of cases. Legionellosis is a collective term for diseases caused by the same organism and, as well as Legionnaires’ Disease, includes milder forms such as Lochgoilhead Fever.
3. The Legionella bacterium is the cause, usually L. pneumophila, but any Legionella species can be involved. In the UK there are usually about 200 cases each year, about half of them contracted abroad. Most cases contracted in the UK are single cases, sometimes without a known source. Large outbreaks with tens of cases and several deaths occur every few years.
4. Any water system can potentially harbour and grow Legionella if the water is between 18-48 oC in any part of the system. To infect people, the water then needs to be dispersed in air as fine droplets, which are then breathed in. Cooling towers are most commonly involved with large outbreaks because they spread high numbers of droplets over a large area.
5. Controlling risk is based on four main measures: keeping water systems clean; keeping water temperatures below 18 oC or above 50 oC; chemical treatment to prevent the organism growing; reducing the escape of droplets. ‘L8’ is HSE’s guidance document on controlling risk, ‘The control of Legionella bacteria in water systems’.
6. Firms with at risk water systems usually employ water treatment contractors to carry out most of the actions required for control. However, the firm retains most of the responsibility and must appoint a responsible person to manage and supervise implementation. Inadequate management, lack of training of staff and poor communication between the firm and its contractor have been identified by HSE as important factors contributing to outbreaks.
7. Cooling towers and evaporative condensers must be registered with the local authority. Control of Legionella in these systems is based on thorough cleaning and disinfection, usually every six months, routine continuous dosing with an ionising biocide such as chlorine or bromine, or a mixture of non-ionising biocides, and careful engineering management of the system. Choice of construction materials and the fitting of a so called ‘drift eliminator’, actually a droplet barrier, are also important.
8. Hot and cold water systems are controlled by ensuring cleanliness, disinfecting after major plumbing work, keeping cold water cold and hot water hot, and possibly by routine chemical treatment such as chlorine dioxide. Other systems such as vehicle washes, industrial spray systems and many others, are controlled in a similar way but rarely need chemical treatment.
9. Checks that the control measures are working are carried out weekly, monthly and quarterly. These include water chemistry tests for cooling systems, temperature readings and bacterial tests. The common bacterial growth test is a ‘dipslide’ – a paddle coated with a solid growth medium which is dipped in the water and then incubated. It grows almost all bacteria – but not Legionella! The growth of any bacteria above a certain number is a good indicator of whether Legionella could grow. Legionella themselves are difficult to grow and need special techniques. The test is useful, but a negative result does not mean that there is no risk.
10. Outbreaks - large or small - are fortunately rare, but the impact of illness and death has a major effect on the firms involved and the surrounding community. During a major outbreak, HSE and other agencies visit all potential sources in an area. If a firm is found to have deficient control measures, they have the powers to take legal action whether or not the system is shown to be part of the outbreak.Niall Evans of Epsilon Training & Consultancy Ltd
