Legionella is a type of bacteria commonly found in natural water sources such as rivers, lakes, and reservoirs. While low levels in the environment are not unusual, the risk increases significantly when Legionella is allowed to multiply in man made water systems.

These systems can include:

• Hot and cold water systems in commercial or residential buildings

• Spa pools, hot tubs, hotel and leisure facilities

• Healthcare water systems such as hospitals and care homes

• Cooling towers and evaporative condensers

When conditions such as stagnant water, warm temperatures, and poor maintenance occur, Legionella bacteria can grow to dangerous levels.

The Health Risks of Legionella

Legionella poses a serious threat to health when inhaled through tiny water droplets (aerosols), such as those produced by showers, taps, cooling towers, or spa pools and hot tubs.

• Legionnaires’ disease – a potentially fatal form of pneumonia that can cause serious illness, especially in older adults, smokers, or those with weakened immune systems.

• Pontiac fever – a milder flu-like illness caused by exposure to Legionella.

Legionnaires’ disease requires urgent medical attention and, in some cases, hospitalisation. This makes prevention and control essential for any organisation operating water systems.

A Brief History of Legionella

The bacteria first came to worldwide attention in 1976, following an outbreak of pneumonia among attendees at an American Legion convention in Philadelphia. The cause was later traced to contaminated water in the hotel’s cooling system. The bacterium was identified and named Legionella pneumophila in reference to the incident.

Since then, outbreaks have been recorded across the globe (including in the UK) often linked to poorly managed water systems. These cases highlight the critical importance of risk assessment, monitoring, and control measures.