Wed 20 Mar 2019
What is it?
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 bacterium Legionella pneumophila and related bacteria are common in natural water sources such as rivers, lakes and reservoirs, but usually in low numbers. But, they may also be found in purpose-built water systems such as domestic hot and cold water systems, spa pools etc.
Where does it come from?
Legionella bacteria are widespread in natural water systems, e.g. rivers and ponds.
The conditions, however, are rarely right for people to catch the disease from these sources. 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, e.g. hot and cold water systems, spa pools, cooling towers and evaporative condensers used in all sorts of premises (domestic, work and leisure).
How do people get it?
People contract Legionnaires' disease by inhaling small droplets of water (aerosols) suspended in the air containing the bacteria. Certain conditions increase the risk from legionella if:
The water temperature in all or some parts of the system is between 20°C - 45°C, which is suitable for growth
It is possible for breathable water droplets to be created and dispersed, e.g. aerosol created by shower heads, water outlets, spa baths
Water is stored and/or re-circulated
There are deposits that can support bacterial growth providing a source of nutrients for the organism, e.g. rust, sludge, scale, organic matter and biofilms
Outlets are used infrequently
The system contains dead ends or unused pipe work, e.g. hot water feed for cold fill only machine
Reducing the risk of Legionella
The risk of Legionella causing illness in small domestic properties is exceedingly low.
Possibly the biggest risk is when you have been away from the property for more than a week e.g. on holiday, or there are additional taps/showers/toilets that are not used daily. Good practice in this situation is simply:
Run the hot water taps (a very unlikely source anyway) for a minimum of 2 minutes
Flush shower heads for a minimum of 2 minutes (to do this, remove from holder before turning on the shower, then hold down over plug hole to lessen risk of inhaling sprayed droplets)
Shower heads should be dismantled and cleaned of scale and debris every 3 months
Keep the hot water on your boiler system at a temperature of minimum 50°C - 60°C WARNING: BE AWARE OF SCALDING!
Flush the toilet twice to circulate fresh water through the system and empty the cistern
The Health and Safety Executive published Guidance on legionnaires disease which advised those ‘in control of premises’ including landlords of residential property, have a legal duty to ensure that the risk posed by legionella bacteria is properly assessed and controlled.
Further advice and information can be obtained on the HSE website: