Legionella – What is it and what harm can it do?

Legionella is the abbreviated name for Legionella pneumophila bacteria. The bacteria is common in natural water sources such as rivers, lakes and reservoirs, but usually in low numbers and where they are less likely to cause any harm. They may also be found in purpose-built water systems such as cooling towers, evaporative condensers, hot and cold water systems and spa pools. In these types of water systems the water temperature is often maintained at the optimum conditions for the legionella bacteria to grow, increasing the risks of Legionnaires’ disease.

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. 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 may be between 20-45 °C, which is suitable for growth
it is possible for breathable water droplets to be created and dispersed e.g. aerosol created by a cooling tower, or water outlets
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

Duties under the Health and Safety at Work etc Act 1974 extend to risks from legionella bacteria, which may arise from work activities. Therefore if you are an employer, or someone in control of premises (e.g. landlord), you have a duty to understand and manage legionella risks, reducing the risk of exposure. All systems require a risk assessment, but not all systems will require elaborate control measures. A simple risk assessment may show that the risks are low and being properly managed to comply with the law.

The Control of Substances Hazardous to Health Regulations 2002 (COSHH) provide a framework of actions designed to assess, prevent or control the risk from bacteria like Legionella and take suitable precautions. Additionally the Approved Code of Practice: ‘Legionnaires’ disease: The control of Legionella bacteria in water systems’ contains practical guidance on how to manage and control the risks in your system.

As the responsible person you must understand how to: