Ireland has seen four out of ten of the warmest years on record over the last decade. Even though we can’t see it, climate change is proven to impact our daily lives and leads to subtle changes in the behaviour of the environment, and water systems. DEFRA launched their 2009 UK Climate Projections based on climate variations, with temperature being one of them. The results indicate that we are likely to see hotter, drier summers and warmer, wetter winters, coupled with extreme weather occurrences such as heat waves and dry spells. As a result, based on the increased likelihood of warmer, wetter conditions, it is possible that Ireland will see an increase in the levels of Legionella bacteria in water systems.

Many argue that an increase in levels of reported Legionnaires cases by the Health Protection Agency is indicative of climate change. Indeed, research has shown that Legionella occurs in systems after hot humid weather. However, Legionella occurs naturally in the environment and if these meteorological conditions are present, it is logical that there is an increased potential for contamination of water sources, which in turn enters man-made systems. With this in mind, and the marked increase in warm humid periods since 2006, it can be argued that the weather will have a definite impact in the future. 

The seasonal variations in reported cases show an increase in August and September, which are detected after the warm and humid months of May and June. Other arguments are that the seasonal variation can be attributed by people behaviour and the holiday season, with more overseas travel than ever before. Indeed statistics show that during summer months people are most likely to go on holiday and the increases would suggest a strong link between infections and visits to hotels and holiday homes. 

Actually, where cases have been reported, usually these are small outbreaks and were not linked, indicating that weather as a source as well as poor awareness by business and hotel owners with regards their responsibility to manage their water systems. Most hotels and holiday homes have peak seasonal usage and unless the owners have a proper Legionella management process in place which involves the routine flushing of unused units and rooms to avoid stagnation, there is a real risk of infection. The ability of legionella to survive and reproduce in poorly maintained water systems is a major threat to the infection of people, leading to Legionnaires' disease.

The association between the environment and human behaviour with case occurrence of Legionnaires, can be linked to the seasonal trends with the use of systems such as fountains, spa baths, showers, domestic hot and cold water systems, cooling towers and air conditioning systems; all of which generate water aerosols and therefore increase the potential source and risk of infection. 

In summary, the recent increase of legionella detection and case occurrences of Legionnaires disease could be attributed to increased climate and seasonal variations. There is a link between increased levels of rainfall and humidity and natural occurrence of Legionella in the environment entering and contaminating man-made water systems. It is only through an increased awareness of legionnaire’s disease and the implementation of management and monitoring of these systems for the deadly bacteria, that will lead to a decrease on reported case occurrences in the future.

Caitriona McEldowney is a senior consultant with Healthy Buildings International, Ireland’s leading Legionella management company.