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Legionella Bacteria

Most people are only aware of Legionnaires’ disease when newspaper headlines have reported an outbreak. In recent years, news items have covered incidents involving air conditioning systems or industrial water-cooling towers. 

Thankfully, this doesn’t happen very often, but what may not be understood is, the bacterium that causes this disease, which is a potentially fatal form of pneumonia, can thrive in other places such as hot tubs, whirlpool baths, compost heaps and even flexible pipe hose tap connectors. 

UK data from 1980 to 2013 shows that there are around 360 cases of Legionnaires’ disease each year, with 30 people dying. Persons most at risk are those with poor immune and respiratory systems such as the elderly, young children and smokers. 

How is it transmitted?

Legionella pneumonophila is the bacterium that is responsible for Legionnaires’ disease. It got its name from the first known serious outbreak in 1976, where a large number of delegates at a USA Legionnaires convention contracted the disease. 

Legionella bacteria are commonly found in water. The bacteria multiply where temperatures are between 20-45°C and nutrients are available. The bacteria are dormant below 20°C and do not survive above 60°C. It is contracted by inhaling small water droplets suspended in the air, known as aerosols.  

Hot tubs and whirlpool baths 

Hot tubs have become very popular in the UK, in fact it’s estimated that 10% of the population has one. Due to the number of people who may use a hot tub, it’s likely to contain a fair amount of organic material in the water. Add to that the fact that the average water temperature is kept at around 40oC and you can see why these conditions can allow bacteria, such as Legionella, to quickly grow. The agitation of the water can produce a fine mist of water, which makes it easy to inhale. 

Whirlpools or spa baths can be another source of infection. Although the water may frequently be changed, stagnant water containing bacteria may remain in the jets and could re-enter the bath when next used.     

In 1999, a Netherlands flower show displayed two new spa pools in exhibition halls for a number of days –­ they became the source of one of the world’s largest outbreaks of Legionnaires’ disease. There were 133 laboratory confirmed cases and 21 people died. It was thought that people inhaled the bacterium as they paused to have a look. 

Advice to consumers

Disinfection, cleaning, monitoring and regular service and maintenance are key factors in controlling Legionella. If you own a hot tub/spa bath you must follow the manufacturers’ instructions. Further information can be accessed at  

Flexible hose pipe tap connectors 

Scientific investigations have shown that some flexible hoses used to connect washbasin taps to plumbing systems are completely unsuitable because the inner surfaces provide ideal places for bacteria to attach and form biofilm (a biofilm is any group of microorganisms in which cells stick to each other on a surface). 

These hoses can provide the right conditions for the growth of Legionella bacteria, however, it should be mentioned that it would be rare for someone to contract Legionnaires’ disease this way. If you are thinking of installing this type of tap connector, ensure that it is WRAS approved. To find out more, please visit

WRAS and Water UK have produced a booklet called Looking after water in your home, which can be viewed on-line here