Legionella bacteria are present in both natural and manmade water systems, and begin to grow when given the correct conditions of temperature and nutrients.
Conditions within water systems that allow the proliferation of Legionella include stagnation within tanks and pipes, temperatures between 20 and 45oC, accumulations of biofouling within pipes, tanks, and calorifiers, and insufficient disinfection techniques. To reduce the risk of legionellosis, steps must be taken to avoid these conditions.
Unfortunately, many common industrial and commercial water services provide the exact conditions that the bacteria require for growth. When Legionella bacteria are present in high numbers in water sprays or droplets, these can be inhaled into the lungs where they cause Legionnaires Disease.
Legionella is transmitted exclusively by inhalation of contaminated water droplets. LP sero-groups one and six are associated with illness in man. The organisms must be present in sufficiently high concentration and must be suspended in aerosol between 3 and 5 microns in diameter. There is no evidence of disease from ingestion of contaminated water or absorption through the skin. High risk areas are therefore associated with showers, sprays, spray taps, taps with high water pressure, and refrigeration and air-conditioning cooling towers.
Legionnaires Disease is similar to a severe form of pneumonia, the symptoms may include breathlessness, coughing, chest aches, headaches and feeling generally unwell. Legionnaires disease has a low attack rate but with a high mortality rate of around 15%.