Legionnaires Disease: What is it and what causes it?

Legionnaires Disease is caused by a bacterium called Legionella pneumophila. Legionella is a common microbe and it is generally found in rivers, lakes and reservoirs, usually in small numbers but is only dangerous when present in a water aerosol, which can be inhaled. The bacterium can then enter the lungs where it proliferates causing a severe pneumonia. One thousand people are treated in hospital for the disease each year. In 12% of cases the disease can prove fatal. Pontiac Fever, and Lochgoilhead Fever are lesser forms of the problem caused by other species of the Legionella.

Water systems, which allow Legionella bacteria to multiply and also produce an aerosol, are considered as high risk. Legionella multiplies best at temperatures around 37 Degrees C. It dies at temperatures above 60 Degrees C. A good source of nutrients also helps the bacteria to proliferate.

This means that water-cooling towers, which operate with warmish water, and broadcast a water aerosol can be considered as high risk and many of the outbreaks where a number of people have been affected result from improperly treated cooling water.

Legionella can also be present in the domestic water system of multi-occupancy buildings like hotels, commercial offices, nursing homes, and hospitals and there is a risk where people shower in water from systems where Legionella proliferation has taken place. In this situation a number of people are likely to be affected.

A recent Government sponsored survey has indicated that sporadic (isolated) cases of Legionnaires Disease are caused by the presence of Legionella in the domestic water system of the patient's home.

Legionella is a problem if it gets into a water system and is allowed to proliferate. L8 (HSE Book - Legionnaires Disease Approved Code of Practice & Guidance) gives guidance on how to stop the bug multiplying in water systems.

Traditional methods have focused on ensuring that water is maintained at the correct temperature and that systems are disinfected periodically. It is for this reason that hot water in most buildings is held at a temperature above 60 Degrees C and hot water taps are labeled as scald risk.

It is the disinfection of water systems, which has proven to be most problematic as the traditional disinfectants, chlorine and chlorine dioxide are not considered reliable in removing biofilm, and Legionella can persist after a disinfection using these chemicals.

The Safewater system uses a chemical, which has proven efficacy against biofilm and therefore Legionella.