Legionnaires' Disease

What is it?
Legionnaires' disease is caused by the legionella pneumophila bacterium and is a type of pneumonia. The bacteria is found in fresh water, warm water environments, cooling towers, hot water systems, whirlpool spa baths, clinical humidifiers in respiratory equipment, supermarket vegetable sprays, natural spa baths, fountains, soil and potting compost. Most of the major outbreaks are associated with cooling towers and large water systems. The legionella bacteria can also cause other flu like diseases such as Pontiac fever and Lochgoilhead fever.

How is it caught and what happens?
Legionnaires' disease can break out if a pathogenic strain of legionella is introduced into the water system, either through contaminated water or contaminated aerosolised water droplets. It is widely accepted that Legionnaires' disease is contracted through inhalation of water droplets infected with the legionella bacterium. Legionnaires' disease does not spread directly from one person to another. However, reports suggest that rarely the bacteria can be aspirated when drinking heavily contaminated water and accidentally inhaling it. Therefore it is essential to maintain a microbiological count of less than (103) - (104). It has also been recorded that on other rare occasions, Legionella counts have been detected within 35 minutes within the mouth of humans who have consumed drinking water. The illness has a low infection rate (around 5%) but a death rate of around 12% (in reported cases), so although risk of infection is quite low, once you display symptoms you must seek medical assistance immediately.

Legionnaires' disease has an incubation period of around 2 - 10 days. Symptoms include loss of energy, high fever, dry cough, aching muscles, headache, chest pains and shortness of breath. As the infection develops it attacks other parts of the chest cavity and most of the body's systems including the abdominal region and the brain. Nausea and diarrhoea can also afflict those infected. If found quickly, Legionnaires' disease is curable, however the disease can kill and those who survive may suffer permanent physical or mental impairment. If you suspect Legionnaires' disease you must see your doctor or go to a local hospital immediately. The illness can be treated by various antibiotics when caught in the early stages.

Who is at risk?
Males are three times more likely to experience the disease than women. Age also plays a part -all genders above 50 years old are at a greater risk of infection. Smokers are at high risk as are people with existing respiratory illness, low immune systems and people on immunosuppressive drugs.

To minimise risk avoid release of water sprays and exposure from possible contaminated water systems. If you are working on air cooling towers or with water systems that may be contaminated, you should use recommended protective methods to protect yourself from inhaling water vapour.

Note: The HSE requires personnel using full cover breathing equipment to be licensed, fully trained and certified.

What conditions encourage the periferation of legionella bacteria?
The following section on the control of legionella has been based on information provided in the Plumbing Engineering Services Design Guide published by the IPHE and "Legionnaires' disease - The control of legionella bacteria in water systems". (Approved Code of Practice ACOP) published by the Health and Safety Executive.

What are the best conditions for legionella to grow?
Legionella can grow at temperatures of between 20-50°C, with the optimum temperature for growth and virulence approximately 36°C. At temperatures below 20°C the bacteria is dormant (it is alive but can't grow) but at temperatures above 60°C legionella is killed with time. Legionella also survives well in humid conditions i.e. the greater the relative humidity the greater the risks.

Nutrients such as rust, sludge, algae and scale will encourage legionella bacteria to grow. Biofilm formation (a thin layer of slime formed by micro-organisms) in water systems provide protection from adverse conditions. The presence of other micro-organisms will, depending on type present, increase the ability of legionella to survive e.g. Flavobacterium will provide nutrients for the legionella to grow on. Legionella can grow inside amoebae, which can encyst, making them (and the legionella inside) very resilient to environmental stress and biocides.

What systems are at the highest risk?
The Approved Code of Practice states that those systems running a higher risk are:

• water systems with a cooling tower;
• water systems with a evaporative condenser;
• hot and cold water systems;
• other plant and systems containing water held at temperatures likely to exceed 20°C and that may release aerosol or spray.
• over stored water systems (cold or hot).

How can Legionella be controlled?
Legionella is present in many water systems. A study by the Public Health Laboratory Service carried out a few years ago found that legionella was present in 60% of man-made water systems. To prevent and control the growth of legionella several steps can be taken:

• ensure that water temperatures fall below 20°C and above 60°C (other issues such as scalding must be addressed);
• control the amount of water spray released into the air;
• avoid the risk of water stagnating – keep pipe lengths short and remove redundant pipework and cisterns;
• keep the system and the water clean to discourage legionella growth;
• avoid materials that encourage legionella growth;
• water should be safely treated in a manner to either kill legionella or prevent its growth.

Cooling towers and systems can be treated with biocides to kill legionella. Biocides should be alternated on a planned basis to ensure a correct bio-control procedure. Other ways to treat legionella include ultra violet radiation, copper ionisation, sliver ionisation and ozone. In hot and cold water systems legionella is typically controlled by storing hot water of above 60°C and distributing it at a minimum return flow temperature of 50°C. Cold water is stored and distributed at below 20°C. Copper and sliver ionisation can also be used as can chlorine dioxide (see dataflow sheet three available to members of the IPHE in the member's only section, or by phoning Joanne Morris on 01708 463112).

An employer's duty...
Employers who manage premises with hot and cold water systems and wet cooling systems have a duty to protect against the risk of Legionnaires' disease. The Employer (or person in control of the premises i.e. landlord) has a duty to have an assessment carried out on the risk of legionella in the water systems of their building. The employer should have an up-to-date plan of the building, a plan on the management of legionella including the control methods, guidance on safe and correct operation of water systems and details on the checks that will be carried out to control legionella. Water systems need to be designed, maintained and operated in a manner which will prevent the growth of the legionella bacterium.

Maintenance records should give a clear indication of the measures taken to avoid Legionnaires' disease and be dated and signed.

The "responsible person"
An employer should appoint a responsible person to manage a legionella control scheme. The responsible person needs to be competent to deal with the scheme and have adequate knowledge and experience of the water system to be able to apply the scheme effectively.

The responsible person and maintenance team have a duty to:

• disinfect all cold water distribution pipework to ensure that every cold water outlet in the building meets the requirements of the disinfectant control technique used in that building;
• all cold water storage cisterns should be regularly inspected, maintained and disinfected;
• a warning notice should be displayed at each water outlet where distribution temperatures of above 50°C are present to reduce the risk of scalding;
• all apparatus likely to produce contaminated aerosols such as humidifiers and cooling towers etc, should be cleaned and disinfected at regular intervals;
• the responsible person should regularly test and inspect all water systems and record all findings in an agreed manner (special attention should be given to shower equipment and spray taps);
• A system should be initiated in conjunction with other staff (administrators, management, cleaners etc) which ensures that if any department rooms or areas are left unoccupied for a week or more, they should be tested before bringing back into service (special attention should be given to shower equipment and spray taps).
• All drinking water outlets should be clearly labelled.

In the UK no chlorination or form of disinfectant is required for existing drinking water mains or outlets, except for initial disinfection in the commissioning of a new building in accordance with BS6700 and the Water Supply (Water Fittings) Regulations 1999. Schedule 2 - Paragraph 3.

Everyone involved in water systems from manufacturers, to designers to those installing and maintaining them, has a duty to prevent the growth of Legionella both legally and morally!

Want to know more?
For information on "System disinfection of hot and cold water services", please contact Joanne Morris and request dataflow sheet three, Tel: 01708 463112, Fax: 01708 448987, Email: joannem@iphe.org.uk.

To purchase the "Plumbing Engineering Services Design Guide" please contact Head Office and hold for an operator, Tel: 01708 472791, Email: designguide@iphe.org.uk

For more information on Legionella please go to www.hse.gov.uk or contact the Health and Safety Executive, InfoLine: 08701 545500, Fax: 02920 859260, Email: hseinformationservices@natbrit.com or write to HSE Information Services, Caerphilly Business Park, Caerphilly CF83 3GG.

To purchase "Legionnaires' disease, the control of legionella bacteria in water systems, approved code of practice and guidance" please visit www.hsebooks.co.uk or you can contact them as follows, Tel: 01787 881165 Fax: 01787 313995, or write to HSE Books, PO Box 1999, Sudbury, Suffolk CO10 2WA.

Thanks go to Jim Walley EngTech LCGI MWNSoc MIPHE RP for his input on this section.