What is Legionnaires’ disease?

Discovered in 1976, Legionnaires’ disease is a potentially fatal form of pneumonia which can affect anybody, but which principally affects those who are susceptible because of age, illness and respiratory problems etc. It is caused by the bacterium Legionella pneumophila and related bacteria. The collective term used to cover the group of diseases caused by legionella bacteria is legionellosis.

Legionnaires’ disease is contracted by inhaling small droplets of water suspended in air which contain the legionella bacterium. The symptoms of the disease are similar to the symptoms of the flu, ranging from high temperature, fever, cough, muscle pains, headaches, loss of coordination and occasionally diarrhoea and vomiting. The illness is treated with an antibiotic called erythromycin or a similar antibiotic. The most severe cases have resulted in death.

Legionella bacteria are widespread in nature, mainly living in natural water systems, eg rivers and ponds. However, the conditions are rarely right for people to catch the disease from these sources. Outbreaks of the illness occur from exposure to legionella growing in purpose-built systems where the water is maintained at a temperature high enough to encourage growth, eg cooling towers, evaporative condensers, spa pools, and hot water systems used in all sorts of premises (work and domestic).

Proliferation of the bacteria typically occurs between 20°C – 45°C and is assisted by the presence of suitable nutrients present in dirt, sludge and scale as well as conditions of poor water flow, stagnation or where dead legs occur in water systems.

On average there are approximately 200–250 reported cases of Legionnaires’ disease each year in the United Kingdom. It is thought, however, that the total number of cases of the disease may be generally underestimated and about half of these cases are associated with travel abroad.