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10 Things everyone should know about Legionnaires Disease and its prevention
The disease was first identified following an outbreak in Philadelphia in 1976 and named after the American Legion (not the French Foreign Legion as many expect), who were holding a convention and whose members were the main victims.
Legionellosis is the collective name given to the pneumonia-like illness caused by legionella bacteria. This includes the most serious Legionnaires’ disease, as well as the similar but less serious conditions of Pontiac fever and Lochgoilhead fever. Legionnaires’ disease is potentially fatal in 10 to 15% of cases and everyone is susceptible to infection. However, some people are at higher risk, including:
people over 45 years of age
smokers and heavy drinkers
people suffering from chronic respiratory or kidney disease
anyone with an impaired immune system.
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.
Any water system can potentially harbour and grow Legionella if the water is between 20-45ºC 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 and showers are most commonly involved with outbreaks, because they produce high volumes of breathable droplets.
Controlling risk is based on four main measures: keeping water systems clean; keeping water temperatures below 18o C or above 50o C; 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’.
Businesses with at risk water systems usually employ contractors to carry out most of the water treatment actions required for control. However, the business retains most of the responsibility and must appoint a responsible person to manage and supervise implementation. Inadequate management systems, lack of training of staff and poor communication between a business and its contractor have been identified by the Health and Safety Executive as important factors contributing to outbreaks on numerous occasions.
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.
Hot and cold water systems are controlled by ensuring cleanliness, disinfecting after major plumbing work, keeping cold water cold, (below 18ºC) and hot water hot, (over 50ºC), and possibly by routine chemical treatments. Other systems such as vehicle washes, industrial spray systems and many others, are controlled in a similar way but rarely need chemical treatment.
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.
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 the HSE and other agencies visit all potential sources in an area. If a firm is found to have deficient control measures, they have the power to take legal action whether or not the system is shown to be part of the outbreak.