Epidemiology

====The transmission of //Legionella pneumophila// involves contaminated water systems disseminating the water as aerosols, sprays, or mists. Legionella transmission occurs via the inhalation of aerosols of contaminated water and is not contagious. This provides direct access for the bacteria to its site of action: the lungs. The likelihood of having the disease depends on the level of contamination in the water source, the susceptibility of the person exposed, and the degree of exposure (Muder //et al.,// 1986). People with compromised defence mechanisms may not be able to fight infection by //L. pneumophila//. Thus smokers and those with chronic cardiovascular or pulmonary conditions are more prone to infection. In addition, people suffering from cancer, diabetes or kidney failure, or those on immuno-suppressant drugs, are also more susceptible to infection as they have an insufficient immune system. (CDC, 2011) ====

====Most outbreaks of Legionnaire’s disease have been associated with poorly maintained artificial water systems. Thus certain preventive measures can be implemented in attempt to control infection by //L pneumophila//. Regular cleaning and disinfection, temperature control, and the addition of biocides all contribute to minimising the growth of the bacteria. Monitoring for scale and sediment build-up, and routine upgrading and repair of the systems is also vital for Legionella control. Ventilation systems in hospitals can also contribute to legionella infection by the airborne route. Thus the use of high-efficiency filters should be used to remove contaminants. Legionella Risk Assessments should be carried out regularly to ensure Legionella control. (EWGLINET, 2005) ====

====Although Legionnaires’ disease occurs worldwide, it is highly under-diagnosed in developing countries and is thus mainly reported from industrialised countries. ==== ====In England and Wales, there are around 400 cases a year. Around 40% of these cases were related to foreign travel (HPA, 2011). ====

====Occurrence rates for Legionnaires’ disease were collected by the European Centre for Disease Prevention and Control (ECDC) from 25 EU countries, Iceland, and Norway for 2009. In total, 5518 cases of Legionnaires’ disease were reported, meaning that 11.2 cases occurred per million (ECDC, 2011). The graph below in Fig.1 shows the occurrence of Legionnaire’s disease cases recorded by ECDC from 1988 till 2007. ====

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==== The establishment of national surveillance systems, research studies, and clinical methods of diagnosis may contribute to the increasing number of cases in certain countries. T he upsurge in cases in 2006 occurred over the summer months, indicating that the disease exhibits a seasonal trend. This could be due to the fact that //Legionella// bacteria thrive in warm water, or because in the summer seasons, people tend to use more aerosol-generating devices such as showers, fountains, and air conditioning units, all of which are potential sources of //L.pneumophila// (Howland & Pope, 1983). ====

==== ==== ====The graph in Fig.2 shows the cases of Legionnaires’ disease by age and gender recorded by ECDC. 77% of these reported cases were people of 50 years of age or older. Even though the risk of acquiring Legionnaires’ disease increased with age in both genders, males were around 3 times more susceptible to infection than females. This could be because males tend to be more exposed to //Legionella//-harbouring sources. ====

**__ References: __**
====CDC. (2011). //Patient Facts: Learn More about Legionnaires' disease.// Available at: http://www.cdc.gov/legionella/patient_facts.htm. Last accessed 8th Jan 2012. ====

====ECDC (2011). //Surveillance report: Legionnaires' disease in Europe 2009.// Available at: [] Last accessed 8th Jan 2012. ====

====EWGLINET. (2005). //European Guidelines for Control and Prevention of Travel Associated Legionnaires' Disease.// Available at: [] Last accessed 8th Jan 2012. ====

====Howland, E.B. & Pope, B.H. (1983) Distribution and seasonality of //Legionella pneumophila// in colling towers. //Current Microbiology// **9**(6) p.319-323 ====

====HPA. (2011). //Legionnaires' disease in Residents of England and Wales - Cases by Month of Onset, 1980 - 2009.// Available: [] Last accessed 8th Jan 2012 ====

====HPA. (2011). //Legionnaires' disease in Residents of England and Wales - Nosocomial, Travel or Community Acquired Cases, 1980 - 2009.// Available: []. Last accessed 8th of Jan 2012 ====

====<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">Muder, R.R., //et al//. (1986) Mode of Transmission of //Legionella pneumophila//. //Archives of Internal Medicine// **146** p.1607-1609 ====

====<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">TRDuk. //Legionella - statistics.// Available at: [] Last accessed 8th Jan 2012 ====

<span style="color: #ff0000; font-family: 'Times New Roman',Times,serif; font-size: 120%;">Excellent work. Well written, clear, relevant and excellent reference and use of referencing protocol.