Legionella Statistics

Escalating Legionnaires’disease cases

The Health Protection Agency’s National Surveillance Scheme for Legionnaires’ disease in residents of England and Wales has been collecting data since 1980. Between 1980 and 2001, there were 150–250 cases reported to the scheme each year. From 2002 onwards, that number has climbed, with over 550 cases in 2006.

Raised awareness

The profile of Legionnaires’ disease has increased in recent years, contributing to an increase in the number of cases diagnosed. In 2002, the largest outbreak of Legionnaires’ disease recorded in England and Wales occurred in Barrow-in-Furness, Cumbria.

Legionnaires’ disease suffers from a high degree of under diagnosis, and there is therefore the potential for increased awareness to lead to an increase in the actual number of cases diagnosed. Hospital Episode Statistics for 2005–2006 showed that over 300,000 cases of community-acquired pneumonia (CAP) were admitted to hospital in England. Of these, over 293,000 were never specified further; studies demonstrate that a significant proportion of these can probably be attributed to Legionnaires’ disease.

Seasonal trends

The unusually high case numbers in 2006 occurred predominantly over the summer months. Cases exhibit a seasonal trend, with peaks occurring between August and October each year. Legionellabacteria thrive in the warmer waters of summer; human behaviours change according to the season so that aerosol-generating devices such as showers and fountains are used more frequently, and cooling towers and air conditioning units come online, with their potential to act as sources. This seasonal increase is seen every year, but was particularly pronounced in 2006. The unexpected speed of the increase in case numbers between July and August 2006, from 43 cases to 119, suggests that increased awareness alone was not responsible for the previous year’s rise in case numbers.


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