History and Background to Legionnaires’ Disease

Legionnaires’ disease is a potentially fatal form of pneumonia which can affect any person, but statistically the risk of contracting the disease increases with factors such as age, illness or immunosuppression, smoking or sex. The disease is caught by inhalation of very fine water droplets, known as water aerosol, which have been contaminated with the bacteria called legionella pneumophila. The higher the growth level, the higher the risk of infection. Legionella bacteria, not just the legionella pneumophila strain, can also cause less serious and non-pneumonic illnesses which are self limiting and not fatal or permanently debilitating, such as Pontiac fever. Legionellosis refers to the contracting of any pulmonary disease associated with any of the 40 plus species of legionella bacteria.
The bacteria are ubiquitous in the natural environment, found in soil and water bodies such as rivers, lakes and reservoirs, usually in low numbers. It should be assumed that legionella bacteria will enter a manufactured water system as there is no requirement for supply companies to provide water that does not contain legionella bacteria. It is the responsibility of the designer, installer, owner and manager of any water system to ensure that this system does not encourage a significant increase in growth.
Conditions and factors that will allow for multiplication of legionella bacteria can be summarised as the following and can all be easily created/provided in a number of engineered water systems:
1) Water Temperatures between 20-45°C.
2) Water Stagnation.
3) Sources of Nutrients – Materials of construction or presence of fouling.
4) Presence of oxygen and light.

Legionella bacteria can survive below 20°C and these water temperatures, even below freezing, will merely aid in reducing growth rates. Above 50°C the bacteria will stop growing and start to die. Above 60°C bacteria will die within a couple of minutes and above 70°C the majority of bacteria will die within seconds.
Large outbreaks of more than 2 or three people, examples being Barrow in Furness in Cumbria in 2002, and the original known outbreaks in the US – at the convention of the American Legion (hence the name) - and also in the UK at Stafford General Hospital, both in the mid 1970’s, are attributed to open evaporative cooling systems. The systems, used to provide cooled water to refrigeration equipment and compressors for air conditioning purposes, through their design create a large amount of aerosol that can be blown several hundred metres. When these cooling towers are therefore located in areas of dense population, the risks of susceptible individuals being exposed to this aerosol increases heavily. These systems are on the whole well maintained through treatment processes and much improved awareness, backed by Local Authority and Environmental Health Office checks and legal requirements for registration of all cooling systems. The Barrow in Furness incident highlighted a break down in contractor services through poor council communication.
The majority of the statistics today (see the information below) highlight domestic and other water systems including spa systems and various water features as responsible for cases of legionellosis within the UK. There is however at present lower awareness of the dangers for these systems.

Statistical Information on Legionnaires’ disease taken from the Health Protection Agency:
(Last HPA review April 2008)
Throughout the 1990’s there have been circa 100-200 cases of Legionnaires’ disease per annum. 2002-2005 consistently found levels above 300 cases per annum.

In 2006 a total of 551 cases were reported
433 male, 118 female
52 deaths
213 cases associated with travel

In 2007 (numbers still to be finalised) a total of 441 cases were reported
328 male, 113 female
53 deaths
198 cases associated with travel
NB: All figures exclude cases of non-pneumonic legionellosis (i.e. Pontiac fever).
As a reminder, these cases are only inclusive of those diagnosed as Legionnaires’ disease.
There are over 180 000 cases of pneumonia each year, sometimes resulting in death, especially in the elderly. Individuals that recover from Legionnaires’ disease do not always return to full physical fitness.

Terminology:
Legionnaires’ disease – A potentially fatal form of pneumonia, one of the illnesses that can be contracted from:
Legionella bacteria – inclusive term for any of the 40 plus species of legionella bacterium, such as Legionella pneumophila, or Legionella micdadei.
Legionellosis – refers to the process of a person contracting an illness as a result of inhalation of water aerosol (tiny droplets not to be confused with vapour/steam) contaminated with legionella bacteria. This could be Legionnaires’ disease, or any of the lesser and non-life threatening illnesses such as Pontiac Fever or Lochgoilhead Fever.

Key Literature:
Health and Safety at Work Act 1974 (HSWA).
Control Of Substances Hazardous to Health regulations 1999 (COSHH).
HSC/HSE L8 Approved Code of Practice (ACoP) – The Control of legionella bacteria in water systems (Third Edition 2000, most recent print 2008).
HSC/HPA - Management of Spa Pools – Controlling the Risks of Infection (2006).
Department of Health – Health Technical Memorandum HTM04-01: The control of legionella, hygiene, “safe” hot water, cold water and drinking water systems.
Health and Safety Executive – Information Leaflet for Providers of Residential Accommodation – INDG376
Health and Safety Executive – Information Leaflet for Controlling Legionella in Nursing and Residential Care Homes – INDG253
The Notification of Cooling Towers and Evaporative Condensers Regulations 1992

back to top