INTRODUCTION

Legionellosis is a 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. Legionnaires' disease is a potentially fatal form of pneumonia, and everyone is susceptible to infection. The risk increases with age, but some people at at higher risk, Including:

  • 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

The bacterium  Legionella pneumophila  and related bacteria are common in natural water sources Such As rivers, lakes and reservoirs, 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.

If the terms are favourable, the bacteria may grow, increasing the risks of Legionnaires' Disease and it is important therefore to control the risks by introducing appropriate measures outlined in  Legionnaires 'disease - The Control of Legionella bacteria in water systems (L8) .

Where does it come from?

Legionella bacteria are widespread in natural water systems, eg rivers and ponds. However, the conditions are rarely right for people to catch the disease from sources such as these. Outbreaks of the illness occur from exposure to Legionella growing in purpose-built systems where water is maintained at a temperature high enough to encourage growth, eg cooling towers, evaporative condensers, hot and cold water systems and pools and spas in all types of premises.

How do people get it?

People contract Legionnaires' disease by inhaling small droplets of water (aerosols), suspended in the air, containing the bacteria. Certain requirements increase the risk from legionella if:

  • the water temperature in some parts of the system may be between 20-45 °C, which is suitable for growth
  • it is feasible for breathable water droplets to be created and dispersed eg aerosol created by a cooling tower, or water outlets
  • Stored water is and/or re-circulated
  • That there are deposits can bacterial growth media providing good source of nutrients for the organism eg rust, sludge, scale, organic matter and biofilms.