Legionnaires' disease - are you protected?01 March 2004

As this issue of Plant Engineer goes to press, a design services manager for Barrow Borough Council is facing seven charges of manslaughter over an outbreak of Legionnaires' disease in August 2002. A further 140 people were infected by the disease, which investigators believe was spread by an air-conditioning unit at an arts centre in Barrow-in-Furness.

The case could mark a watershed in health and safety prosecutions. In the past, it has been unusual for successful prosecutions to be brought against middle managers in larger organisations, because of the difficulty of establishing culpability within complex management structures. So it's clear that anyone with responsibility for the safe upkeep of plant and equipment that could spread the disease needs to be on their guard.

After all, the Barrow case was not an isolated incident. In February, a man being treated for cancer died of Legionnaires' disease at a hospital in Bath. Last autumn, an outbreak in Hereford killed two people in their 70s and affected 24 others. This was traced back to a cider factory.

Also known as legionellosis, the disease takes its name from its first outbreak in 1976, which killed 29 American Legion members at a convention in a Philadelphia hotel. Since then, cases have been reported throughout the world. The disease is contracted by the inhalation of airborne water droplets, containing Legionella bacteria, in aerosol form. (Other means of infection have yet to be substantiated.) The bacterium - Legionella pneumophila (from the Greek for lung-loving) - is normally found in warm water environments, although it has even been found in soil. Researchers say that the organisms can usually survive in a wide range of damp conditions: between 0 and 63°C, in pH of 5.0-8.5, and in dissolved oxygen concentrations of 0.2-15 ppm in water.

The organisms can form a bio-film and attach themselves to a variety of surfaces - including plastics, rubber and wood - where they can colonise. Organic sediments, scale and inorganic precipitates can also provide Legionella with a surface on which to attach, and can also become a protective barrier against treatment. Organic sediments can also stimulate the growth of other organisms which in turn form by-products that can also stimulate Legionella growth.

Temperature appears to be crucial to the rate of multiplication, although different sources quote various effective temperatures. However the ideal situation for reproduction is in warm, somewhat stagnant water, as in many types of plumbing systems and hot water storage facilities. Other types of water-containing systems are also vulnerable, given the appropriate conditions. These include cooling towers, open evaporative condensers, air conditioning systems (both large and portable), spa baths, showers and swimming pools. Adequate precautions are therefore a necessity.

It is obvious therefore that one must be extremely vigilant against Legionella wherever water is stored, distributed, used or discharged - whether in industrial, commercial or domestic situations. Following an outbreak of the disease, investigation usually begins around wet cooling systems, cooling towers and evaporative condensers - although investigation of the sufferers' movements may also draw attention to water sprays, such as showers.

Evaporative cooling systems have their own peculiar problems in the context of Legionella. In most cases, the operation of any such system can inherently lead to the ideal conditions for microbiological growth, by creating water-borne vapours. Fortunately, modern water cooling towers are designed to minimise the carry-over of water vapour, to reduce the operating burden on the user.

However, a number of other areas need detailed management and control: water conditions, chemical additions and equipment maintenance can all lead to environmental problems.

The plume of any moisture-laden air discharge may affect not only the people employed in the associated premises, but also the general public nearby. The area covered by the air drift will vary considerably depending on the weather conditions, local topography and of course the plume velocity from the equipment. Before any new installation, it is essential that specific water treatment, testing and control are planned well in advance.

All buildings and installations, even offices and domestic premises, should come under scrutiny and control. There is no blanket solution for all installations and systems, because of the variety of equipment, locations, situations, buildings and industries. However, the box item 'General precautions' on the previous page gives a broad outline of the various steps that should be taken.

Cooling towers

Where water cooling towers are concerned, Legionella protection is not the sole reason why it is essential to control the water condition. Evaporative cooling brings with it a concentration of solids. To maintain a clean system, regular blow-down systems should be employed. This will also keep control over any by-products brought about by the introduction of water treatment chemicals and other additives.

Each and every tower is bound to be different, in its use, temperature, and circulating conditions and situation, so they have to be treated as entirely separate items of equipment, in every respect. However, it is fair to say that the likelihood of Legionella infection can be best reduced by good engineering practices in the operation and maintenance of air and water handling systems.
- Cooling towers and evaporative condensers should be inspected and thoroughly cleaned at least four times a year.
- Corroded parts, such as drift eliminators, should be replaced.
- Algae and accumulated scale should be removed.
- Cooling water should be treated constantly. Ideally, an automatic water treatment system, that continuously controls the quality of the circulating water by routine injections of the appropriate chemicals, should be used.
- Fresh air intakes should not be built close to cooling towers, since contaminated water particles may enter the ventilation system.
- If you do not have fully qualified chemists available on site, then adopt the professional approach and employ a reputable water treatment organisation to carry out routine tests and to advise on preventative and water maintenance procedures.

Legislation

There are a number of pieces of legislation that apply to the prevention of Legionnaires' disease. Risks from Legionella arising from work activities fall within the remit of the Health & Safety at Work Act (HSW). In addition, harmful microorganisms are subject to the Control of Substances Hazardous to Health Regulations 1999 (COSHH), which sets out requirements for risk assessment and measures to prevent or adequately control exposure. The Management of Health and Safety at Work Regulations 1999 (MHSWR) are also important with respect to management arrangements.

The Approved Code of Practice (ACoP) (L8) Legionnaires' Disease: the control of Legionella bacteria in water systems provides a basic framework for preventing outbreaks of the disease, and gives advice on the requirements of HSW, COSHH and MHSWR. The ACoP sets out the responsibilities of various parties, including manufacturers, importers, suppliers and installers of products and services. Employers' duties are to:
- Identify and assess risks from Legionella;
- Manage the risks, including the appointment of a person to take managerial responsibility and to provide supervision and training of personnel;
- Avoid the use of systems that give rise to a reasonably foreseeable risk of Legionella or, where this is not reasonably practicable, prepare a written scheme for minimising the risk of exposure;
- Implement, manage and monitor the scheme of precautions; and
- Keep appropriate records.

Occupiers of premises also have a duty under the Notification of Cooling Towers and Evaporative Condensers Regulations 1992 (NCTEC) to notify the local authority, in writing, of details of notifiable devices. These comprise cooling towers and evaporative condensers, except where they do not contain water, or their water or electricity supply is not connected. The main purpose of this notification is to assist when investigating outbreaks.

Symptoms and treatment

Legionnaires' disease has no very obvious features to distinguish it from other forms of pneumonia; it can only be formally identified through laboratory tests. It usually develops within two to ten days of exposure to Legionella bacteria. People with chest problems and heavy smokers may be particularly vulnerable. The disease is not regarded as contagious.

A cough may be the very first sign of the lung infection, which may become severe, and stomach disorders with diarrhoea are another possible symptom. The sufferer may experience loss of energy, headaches, nausea, aching muscles, a high fever (often exceeding 104°F (40°C)) and chest pains. A number of other bodily functions, include mental faculties, may also be affected. The disease can cause death from high fever. Survivors may also suffer from permanent physical or mental impairment.

Fortunately, antibiotic treatments such as erythromycin and azithromycin can be very effective, especially if the disease is diagnosed early.

The disease is fatal in 5-15% of cases: the uncertainty in the figures arises because some cases may not be correctly diagnosed. The United States Center for Disease Control and Prevention in Atlanta has estimated that 10,000-15,000 people may be infected each year.

Legionella can also cause another flu-like illness, Pontiac fever, but this is far less serious. Most people infected usually recover within a few days, without necessarily having to be treated in hospital.

How is the disease spread?

- The disease is contracted by the inhalation of airborne water droplets, containing Legionella bacteria, in aerosol form

- The Legionella pneumophila bacterium is normally found in warm water. Organisms can usually survive in a wide range of damp conditions

- The organisms can form a bio-film and attach themselves to a variety of surfaces - including plastics, rubber and wood - where they can colonise - Organic sediments, scale and inorganic precipitates can provide Legionella with a surface on which to attach, and can also become a protective barrier

- Organic sediments can also stimulate the growth of other organisms, which in turn form by-products that can also stimulate Legionella growth

- The ideal situation for reproduction is in warm, somewhat stagnant water, as in many types of plumbing systems and hot water storage facilities

General precautions

- Carry out a risk assessment of all engineered water systems, including cooling towers, hot and cold water storage and distribution systems, including sprays, showers, spa baths and swimming pools.

- Perform a very detailed evaluation of all air-conditioning units - and in particular their air outlets and any form of condensed water discharge. Probably the most neglected units are the portable air-conditioning units, which are now used quite frequently in office and domestic environments. Ensure the container of condensed water is emptied frequently, rather than being left to overflow onto the floor.

- Provide a plan to carry out remedial works to high-risk areas.

- Provide a programme for cleaning and disinfection of water systems.

- Set up a full maintenance schedule, to provide good water conditions throughout the plant or building. Depending on the system, this could involve heat treatment or biocide dosage.

- Set up a monitoring scheme to demonstrate the effects of the maintenance programme. Perform regular analytical evaluations and take follow-up action as required.

- Maintain a record system to demonstrate that the required actions have been taken and have been successful in reducing the risk of the Legionella bacterium.

References and further information

Health and Safety Executive
Phone: HSE Infoline, 08701 545500
Email: hseinformationservices@natbrit.com

Publications:
Legionnaires' Disease: The control of Legionella bacteria in water systems. Approved Code of Practice and Guidance L8, 2000 (ISBN 0 7176 1772 6). Available price £8 from HSE Books, PO Box 1999, Sudbury, Suffolk, CO10 2WA. (Tel: 01787 881165. Fax: 01787 313995. See www.hsebooks. co.uk)
- To complement the ACoP and Guidance, a short and simple free leaflet has been produced: Legionnaires' disease: A guide for employers - IAC27 (rev2). Available at www.hse.gov.uk /pubns/iacl27.pdf or by post from HSE Books
- The ACoP is evaluated in HSE Research Report RR140. See www.hse.gov.uk/research/rrhtm/rr140.htm Web: www.hsedirect.com provides instant access to the latest legislation, ACoPs and current guidance.

The Health Protection Agency Established in 2003 with responsibility for England and Wales, the HPA protects the population from infection. It works with others to control and prevent the spread of infectious diseases. Its website is at www.hpa.org.uk

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