Causes of Legionnaires' Disease

What Causes Legionnaires’ Disease?

The Legionella bacteria responsible for Legionnaires’ Disease is found naturally in fresh water sources such as rivers, lakes and reservoirs, but very rarely in the quantities or format that causes the disease. Any man-made water system that has a water temperature between 20 and 45 centigrade, that stores or recirculates water or has the capacity to create or spread breathable droplets of contaminated water (water vapour) can be a source of Legionnaires’ Disease. The most common sources are air-conditioning systems, hot and cold-water systems, and spa baths, but any devices such as humidifiers, air-washers, showers or even ornamental fountains can be a source of the disease.

When large outbreaks of the disease occur, it is commonly found to have originated within air-conditioning systems that can distribute the contaminated water vapour through large areas. The disease is synonymous with hotels, cruise ships and hospitals – all situations where centralised air-conditioning systems have the capacity to spread the bacteria throughout the building, or local area.

Since the first recognised outbreak at the Bellevue-Stratford hotel in 1976, subsequent large-scale outbreaks have occurred in hospitals and nursing homes around the world, and in many cases the source of the contamination was found to be the cooling towers within air-conditioning systems. The combination of perfect growing temperatures and a food source for the bacteria; rust, sludge, mould and other organic matter, make these systems perfect breeding ground for the Legionella bacteria.

Once the bacteria have the chance to breed, they can be spread around the building, throughout the water system including showers and taps. When outbreaks occur in hospitals the effect can be even more devastating as many of the patients are likely to have reduced immune systems, giving the body less of a chance to fight the infection.

In other situations an outbreak of the disease can be relatively isolated; for example if a hot tub or spa bath is not properly cleaned or maintained then the bacteria may develop within the water. The water temperature within these is ideal for the bacteria to grow, and the steam and splashing around can allow tiny droplets of the water, containing the bacteria, to be inhaled.

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