Legionairres' disease is a type of pneumonia, caused by Legionella Pneumophila bacteria, a naturally ocurring bacteria commonly found in natural water sources such as rivers, lakes and reservoirs, but usually in low numbers.

They may also be found in purpose-built water systems such as cooling towers, evaporative condensers, hot and cold water systems and spa pools, where temperatures are often higher.

If conditions are favourable, LP bacteria may grow rapidly increasing the risks of Legionnaires’ disease and it is therefore important to control the risks by introducing appropriate measures outlined in The Control of Legionella Bacteria in Water Systems (ACOP L8 2013), and HSG 274 Pts 1,2 & 3.

Those more at risk include:

Conditions favouring growth:

  • people over 45 years of age
  • smokers and heavy drinkers
  • people suffering from chronic respiratory or kidney disease
  • diabetes, lung and heart disease
  • anyone with an impaired immune system
  • Presence of nutrients such as scale, sediment, corrosion products, & biofilm
  • Temperatures of 20 - 45°C
  • Areas of low flow rates or stagnation, such as deadlegs.

While over 40 'serogroups' of Legionella Bacteria have been identified, Legionnaires’ disease is most often associated with Legionella Pneumophila Serogroup 1. Everyone is susceptible to infection to some extent. 

Pneumonia results in about 100,000 hospital admissions each year in England, but the exact cause is rarely investigated. 

Legionellosis is the collective term for diseases caused by legionella bacteria including the most serious - Legionnaires’ disease, as well as the similar but less serious conditions of Pontiac fever and Lochgoilhead fever. 

Legionella Bacteria multiplies in water temperatures of 6 - 45 degrees Celcius, and most rapidly at 37 degrees.

Before any formal health and safety management system for water systems is implemented, the duty holder should carry out a risk assessment to identify the possible risks. The purpose of the assessment is to enable a decision on: (a) the risk to health, ie whether the potential for harm to health from exposure is reasonably foreseeable, unless adequate precautionary measures are taken; (b) the necessary measures to prevent, or adequately control, the risk from exposure to legionella bacteria.

 ACOP L8 2013 and HSG 274 Pts 1,2 & 3 are available as free downloads from the HSE website. Yes we do mean free!

HSG 274 Pt 1 applies to Evaporative Cooling Towers and Evaporative Condensers - 'Open Cooling Systems'

HSG 274 Pt 2 applies to Hot and Cold water systems, often referred to as 'Domestic' systems even though they are in a commercial environment.

HSG 274 Pt 3 applies to all other water systems.

Contains public sector information licensed under the Open Government Licence v2.0


Some significant facts and figures about Legionairres' Desease

  • 1948 the oldest isolated case of Legionairres' Disease.
  • 1976 saw the first outbreak, at Belle Vue Hotel in Philadelphia, USA. 234 ill, 34 fatalities. LP traced to cooling tower.
  • 1978 first identified case of L.D in the UK at Corby.
  • 1979 Oxford: 2 ill. LP traced to showers.
  • 1980 first hospital outbreak at Kingston. 12 ill, 3 fatalities. L.P. was found in the rubber washers in shower fittings
  • 1983 University Hospital: 35 ill. LP found in water outlets.
  • 1984 Glasgow: 33 ill, 1 fatality. LP traced to a cooling tower over a mile away.
  • 1985 Stafford District Hosp: 103 ill, 28 fatalities. LP traced to their cooling tower.
  • 1988 BBC Broadcasting House: 43 ill, 2 fatalities. LP traced to their cooling tower.
  • 2012 an outbreak in south-west Edinburgh. 92 ill, 4 fatalities believed to be from this outbreak. LP traced to cooling tower.
  • 2013 Rotherham: 1 person died. LP traced to a fixed showerhead in a health spa.  Read more about this.

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