Legionella Risk Assessment Services

Legionnaires’ disease or Legionellosis is a potentially fatal form of pneumonia. People may get infected when they breathe in tiny water droplets (aerosols) or droplet nuclei (particles left after the water has evaporated) contaminated with elevated concentrations of Legionella bacteria.

Legionella bacteria grow best between temperatures of 20°C – 45°C, with optimum growth temperature being 35°C – 40°C. High temperatures (minimum 60°C) usually kill the bacteria.

Legionella bacteria are found in low numbers in natural aquatic environments, for instance, lakes, rivers and groundwater. As a result, it is virtually impossible to prevent Legionella bacteria from entering man-made water systems.

In low numbers, the bacteria are generally considered harmless. With the correct conditions, for example, warm water, the presence of micro-organisms and nutrients in the water or materials such as rust, these bacteria can grow and multiply to high levels which increase the risk of exposure.

The bacteria tend to grow in biofilms (slime). Biofilms are likely to form on surfaces where there is low water flow or water is allowed to stagnate. However, the growth of Legionella bacteria can be controlled.