What is Legionnaires' disease?

Legionnaires' disease is a severe form of pneumonia caused by inhaling small droplets of water contaminated with Legionella bacteria. While the bacteria are naturally present in rivers, ponds and other water sources, the disease usually arises when they grow in man-made water systems that provide ideal conditions; warm temperatures, stagnant water, and areas where scale, sludge or biofilm can accumulate.

People can contract Legionnaires’ disease from systems that generate aerosols, such as showers, taps that are rarely used, hot tubs, cooling towers and large air conditioning systems. The risk of infection is higher for certain groups, including people over 45, smokers, heavy drinkers and individuals with weakened immune systems or chronic illnesses such as diabetes, heart, lung or kidney disease.

Symptoms often begin like the flu, with fever, chills, headache, muscle aches and a persistent cough. In more serious cases, it can progress to pneumonia, shortness of breath, chest pain and even confusion. Early diagnosis is important, as treatment typically requires antibiotics, sometimes administered in hospital for severe cases. Most people recover fully, but it can take several weeks to regain full health.

Because Legionnaires’ disease is not spread from person to person, controlling the growth of Legionella in water systems is crucial. Proper system design, regular maintenance and using qualified plumbers are key steps to reduce the risk and protect both homeowners and business occupants.

For practical guidance on keeping your home or business safe, including tips on flushing water systems, cleaning taps and showerheads and maintaining correct water temperatures, read our guidance on how to prevent Legionnaires’ disease in your home or business. Following these steps can significantly reduce the risk of Legionella bacteria establishing in your water systems.