What is Legionnaires’ Disease?
Legionnaires’ disease is a potentially fatal form of pneumonia which can affect anybody, but which principally affects those who are susceptible because of age, illness and immunosuppression etc. It is caused by the bacterium Legionella pneumophila and related bacteria.
Legionnaires’ disease is contracted through inhaling Legionella bacteria, either in droplets of water suspended in the air (aerosols), or in the particles left after the water has evaporated.
The symptoms of Legionnaires’ disease include fever, chills, cough, muscular pain, headache, diarrhoea and mental confusion. However, not everyone exposed to Legionella becomes ill, and some may simply present with a mild influenza-like infection. On average, there are approximately 200-250 reported cases of Legionnaires’ disease each year in the UK although this is likely to be higher due to wrongly diagnosed cases of pneumonia. About half of these cases are caught abroad. The other half are the result of infections acquired in the UK.
In approximately 12% of reported cases, infection with Legionella bacteria is fatal. The level of fatalities is significantly higher among identified risk groups. Although it can affect anyone, certain groups are more susceptible, including the very young, people over 45 and people already suffering from an illness – especially cancer or diabetes, people with a weakened immune system, smokers and alcoholics. Men also appear to be more susceptible than women.
What are the Sources of Risk?
Legionella bacteria are common and can be found naturally in water sources such as rivers, ponds and reservoirs, usually in low numbers. Outbreaks occur when the bacteria colonise manufactured water systems where temperatures are suitable to encouraging bacterial growth.
Legionella bacteria can thrive in man made water systems given the correct water temperatures and a supply of nutrients. They can survive at temperatures ranging from 6°C to 60°C. They can remain dormant at low temperatures and multiply readily at temperatures between 20°C and 45°C. They are at their most virulent at 37°C.
The bacteria also require a source of nutrients in order to multiply. These are derived from a wide variety of sources, including algae, amoebae, sediment, sludge, scale, corrosion by-products, biofilms and other bacteria.
Therefore, anywhere where water is stored or used between the temperatures of 20°C and 45°C, that also offers a supply of nutrients, is a potential breeding ground for Legionella bacteria. Where infected water is formed into a spray or mist, the risk of inhalation and infection is significant.
Areas of particular concern are:
- Water systems involving a cooling tower or evaporative condenser;
- Air conditioning systems, especially those incorporating humidifiers or air washers;
- Hot and cold water systems;
- Spa baths, Jacuzzis and other pools in which water is agitated and re-circulated;
- Other systems where water is stored between the temperatures of 20-45°C and which produce an aerosol or spray.
The control of Legionella in the UK is governed by strict government guidelines and statutory responsibilities directed by law. Our guide to Legionella legislation identifies the legal duties imposed on employers and those responsible for the control of premises where water is used or stored.
