Legionnaires’ Disease Outbreak

A recent outbreak of Legionnaires’ Disease in Edinburgh, which started at the end of May, has officially been declared over by health officials.  100 cases of the disease have been confirmed leading to 3 fatalities but the cause of the outbreak is still to be determined.  Cooling towers in the south of the city have been pinpointed as the likely culprits but HSE investigations remain on-going.  Improvement Notices have been issued by HSE Inspectors to some premises with cooling towers.

The news of the first case broke on 31 May with further cases confirmed in the following 48 hours.  It caused alarm and was in the headlines for a number of weeks but what is Legionnaires’ Disease?

The Bacteria:

Legionella is a naturally occurring bacteria which is common in rivers and ponds where it does not cause much of a problem.  However, as the bacteria is relatively widespread it can contaminate man-made water systems such as cooling towers and hot and cold water services.  The bacteria thrives in temperatures between 20 and 45°C, especially if the water is stagnant and there is a ready supply of nutrients available from rust, scale, algae etc.  The bacteria can survive low temperatures but are killed by high temperatures.

Legionnaires’ Disease

The legionella bacteria is only dangerous to people if contaminated water droplets are released as a spray and inhaled.  If the bacteria is inhaled it can lead to a severe pneumonia known as Legionnaires’ Disease (named after an outbreak which affected the American Legion in the 1970s).

Not everyone who inhales the bacteria becomes ill – in fact most people exposed do not show any sign of illness.  Men are at a slightly higher risk than women and it usually affects older people or those with underlying serious medical conditions.  Illness is very uncommon in people under the age of 20.  Smokers are at an increased risk as is anyone who has respiratory problems or suffers from an immunity deficiency.

Legionnaires’ disease cannot be spread from one person to another.  Other similar (but usually less serious) illnesses include Pontiac Fever and Lochgoilhead Fever.  Collectively the illnesses that the legionella bacteria causes are known as “Legionellosis”.

How to Manage the risk.

Controllers of premises (e.g. employers or landlords) must:

  • Identify sources any potential sources of legionella risk.
  • Prepare a scheme for preventing and controlling any risk.
  • Appoint a ‘responsible person’ to implement and manage the scheme.
  • Keep records of the measures taken.

If it is determined that there is a significant risk from legionella then appropriate control measures must be taken to negate that risk.

Control strategy:

In the first instance consideration should be given to preventing the risk of legionella by examining the type of water systems that are in place.  For example, could a wet cooling system be replaced by a dry air cooling system.

If it is not possible to completely eliminate the presence of legionella bacteria from within a water system then the primary aim of any control strategy should be to promote conditions that control bacterial growth and spread.

The HSE guidance on legionella recommends that:

  • Hot water should be stored above 60°C and distributed above 50°C (although at taps water should not be so hot that there is risk of scalding)
  • Cold water should be kept stored below 20°C.
  • Conditions which are favourable to the growth of legionella and other bacteria should be avoided throughout the water system.
  • Pipe-work should be as short in length as possible to prevent any water from stagnating.  Pipes that are no longer used should be removed.
  • Where water spray is released it must be properly controlled.
  • Water systems should be cleaned regularly.
  • Where necessary, water should be treated to kill legionella and/or restrict its growth.

Water treatment:

Normal treatment methods include chlorination, copper/silver ionisation and using biocides – all of which are designed to kill and control bacteria.  Such treatments must only be carried out by competent persons.

If water is treated it does not mean that water temperature control and other preventative measures should be discontinued.

Whatever method of treatment is used it is important to monitor it in order to ensure that it is effective.


Sampling is the most common way of testing if there is any legionella bacteria present in water – i.e. establishing if control measures are working as they should.

However, sampling does require specialist expertise to ensure that the results are accurate.

For more information or advice on Legionella risks and control measures, please contact The Compliance Group.

The HSE website has a dedicated Legionella section which may be of interest: http://www.hse.gov.uk/legionnaires/index.htm