Winter Legionella risk: why cold weather increases exposure

What is legionella?

Legionnaires’ disease is a potentially fatal form of pneumonia caused by the inhalation of water droplets containing legionella bacteria. Legionella bacteria can be found in natural water sources but most commonly, legionella infections occur as a result of a person being exposed to the bacteria that has been allowed to proliferate in purpose-built water systems such as air conditioning units, humidifiers, hot and cold water systems, water tanks and showers and taps that are infrequently used. 

What causes it?

There is an increased risk of legionella bacteria in systems where water is stored or recirculated (such as central heating systems with water tanks and air-cooling systems) and where other environmental conditions are met. Systems that are poorly maintained and where rust, sludge or other organic matter has been allowed to collect will support the growth of legionella bacteria, further increasing the risk. Legionella bacteria thrive in water temperatures that are between 20 and 45°C.  If contaminated water has an outlet which could produce water droplets or aerosols, for example a tap, shower or vent, then this would mean anyone in the immediate vicinity of those outlets will potentially be exposed to the legionella bacteria and therefore exposed to a risk of developing Legionnaires’ disease from a legionella infection. 

Who is at risk?

Anyone that inhales the bacteria is at risk of infection, however, people over the age of 45 or those with compromised immune systems, chronic respiratory or kidney diseases or lung conditions are particularly vulnerable. Care homes, healthcare settings and any other settings which are used or occupied by medically vulnerable individuals are therefore considered to be high risk for bacteria exposure. 

Who has duties in relation to Legionella risk under health and safety legislation?

Employers and any person who has responsibilities for the control of premises (including landlords) have duties under various regulations and health and safety legislation to take reasonably practicable steps to protect their employees or other persons using their premises from the risk of exposure to legionella bacteria. Employers also have additional duties to ensure the safety of their workers whilst they are at work, and this will extend to work activities that are being carried out at sites which are not within the control of the employer.

What can duty holders do to control the risk?

The two main ways to control the risk of legionella infection is firstly to maintain water systems in such a way that legionella bacteria are not allowed to proliferate and secondly to reduce, as far as is reasonably practicable, the exposure of persons to water droplets or aerosols from those systems. 

If you are an employer or person with control over a premises, then in order to meet your duties in relation to the prevention of exposure to legionella bacteria then you must do the following:

• Carry out a suitable legionella risk assessment of all your purpose-built water systems and establish whether they are likely to present a risk of exposure to legionella bacteria;
• Ensure that the person carrying out the risk assessment is competent to do so, this would mean that they should understand the water system and its constituent parts, be able to understand the risk factors of legionella, identify if they are present and be able to take appropriate control measures if a risk is identified;
• Where a risk of legionella bacteria exposure has been identified then control measures must be put in place.

The starting point is to always consider whether the risk can be eliminated altogether. For example, can the water system be replaced with another system that does not carry a risk of legionella bacteria exposure? If not, then you would need to consider what other reasonably practicable steps can be taken to reduce the risk, for example:

• Ensuring proper maintenance of the water system to avoid conditions that support the growth of legionella bacteria;
• Not allowing water to sit stagnant anywhere in the system;
• Removing redundant pipework and draining unused water tanks;
• Monitoring the temperatures that water is stored at to ensure, where practicable, that it is not within the range that supports legionella growth (e.g. stored over 60°C);
• Implementation of a regular maintenance programme

The types of control measures that you choose to implement will vary depending on the type of water system that is being assessed. 

You should keep a written record of the risk assessment and control measures in place to reduce the identified risks. It is also important to remember that risk assessments should be reviewed and updated regularly and as a minimum when there have been changes to the water system, its use or significant changes to the building or the building’s use since the last risk assessment or in any other circumstances which leads you to believe the risk assessment is no longer valid. 

Why can it be harder to manage legionella risk over winter?

It can be more difficult in winter to manage legionella risk due to a number of factors. With winter comes colder temperatures; if the water in water systems is not maintained at an appropriate temperature, then the system will become more vulnerable to legionella bacteria growth. Some buildings, or parts of buildings such as seasonal leisure facilities, universities and hospitality venues, may become unoccupied over the winter months leading to water systems being left unused for long periods of time with water stagnating which is conducive to legionella growth. The reactivation of heating systems after periods of dormancy can disturb biofilm and sediment which has built up in the system which further increases the risk of legionella bacteria. It is therefore important that extra precautionary steps are taken, to reduce the increased risks posed by colder temperatures or other winter preparations over the winter months to ensure compliance with your duties.