6.1 Background

Legionnaires’ disease was first identified in 1976 in Philadelphia, USA, amongst individuals attending a state convention of the American Legion, which led to the naming of the condition. One hundred and eighty members of the convention developed a severe pneumonia and twenty-nine people died ⁽¹⁾. The first major outbreak recorded in the UK occurred in Staffordshire associated with the District General Hospital in 1985. One hundred and one people were affected and 28 individuals died ⁽⁹⁾. The largest single outbreak reported in the UK was in Barrow-in-Furness, where 172 people were affected and 7 people died.

The bacterium that causes Legionnaires’ disease, Legionella pneumophila can cause a severe pneumonia with death occurring in 10-15% of cases. A milder form of the disease may occur without the pneumonia, named Pontiac Fever, with symptoms like a mild influenza illness. It usually takes between 2-10 days for the disease to develop. The disease can be treated with antibiotics ⁽⁶⁾.

The bacterium lives naturally in warm water (32-45°C), for example in: hot and cold water systems, fountains, spas, the water in air-conditioning units and cooling towers. Individuals contract the disease by breathing in aerosols from a contaminated source and not by person to person spread ⁽²⁾. Prevention is through good maintenance of water systems, in particular air-conditioning and hot water systems.

6.2 Surveillance

Legionella pneumophila can be detected through blood or urine tests. Legionnaires’ disease is not a statutory notifiable disease in the UK. Initial information about cases is obtained from clinicians treating suspected cases or through laboratory confirmed reports and given to local Health Protection Units. Individuals are then followed up by case questionnaires to obtain information on their occupation, daily movements and any significant travel away from home during the incubation period. This will aid identification of common exposures and potential environmental sources. Implicated sources are then decontaminated. This can involve investigations by the Health and Safety Executive. In the USA Legionnaires’ Disease is a notifiable disease in the majority of states but because of under diagnosis and under reporting Centre for Disease Control are then and Prevention (USA) estimate only 2-10% of cases are actually reported ⁽³⁾

As well as surveillance occurring in England by the Health Protection Agency (HPA) there is a European wide surveillance system. The European Working Group for Legionella Infections (EWGI) was established in 1986 and is currently hosted at the Centre for Infections (HPA) in Colindale, London. The aims of this group are to improve the knowledge and information surrounding the disease ⁽⁵⁾. This network has enabled rapid communication of suspected clusters so that coordinated responses can be planned and implemented, but despite this outbreaks are often difficult to control ⁽⁸⁾.

Epidemiological Surveillance Data

6.3 Temporal Trends

The number of reported cases of Legionnaires’ disease has been increasing over the last two decades in Europe and England and Wales. This could be due to a real increase in cases however; it may also be due to improved diagnosis and testing with the advent of urinary testing and better reporting to the surveillance systems. Outbreaks cause considerable media interest but the majority of the cases in the UK are sporadic with no links between individuals determined and no source identified.

Figure 6.1: Number of cases of Legionnaires' Disease occurring in Europe reported to EWGLI from 1987-August 2006

Number of cases of Legionnaire’s Disease occurring in Europe reported to EWGLI from 1987-August 2006

The number of cases in the West Midlands has increased from 28 reported cases in 1994 to 50 in 2005, incidence rates of 5.3 and 9.4 per million respectively ⁽⁸⁾.

Figure 6.2: Incidence rate (per million) of Legionnaires’ disease in England and Wales compared to the West Midlands

Incidence rate (per million) of Legionnaires’ disease in England and Wales compared to the West Midlands

Seasonal trends are observed with a peak usually occurring in late summer and early autumn.

Figure 6.3: Reported cases of Legionnaires’ disease in residents of the West Midlands, Cases by Month of Onset 1994-2005

Reported cases of Legionnaires’ disease in residents of the West Midlands, Cases by Month of Onset 1994-2005

6.4 Case Demographic Trends

Legionnaires’ Disease is more common in males than females across all age- groups and primarily affects males in the 50-59 year age group. It is very rare in those under 20 years of age. The disease is more common in patients who smoke and those who have weakened immune systems and chronic lung and renal diseases.

Figure 6.4: Legionnaires’ disease in Residents of the West Midlands by Gender, 1994-2005

Legionnaires’ disease in Residents of the West Midlands by Gender, 1994-2005

Occupation was only available for 297 case of Legionnaires disease in residents of the West Midlands. These are shown in Table 6.1.

Table 6.1: Occupation of patients with reported cases of Legionnaires’ disease in residents from the West Midlands 1994-2005

Occupation of patients with reported cases of Legionnaires’ disease in residents from the West Midlands 1994-2005

6.5 Geographical Trends

European surveillance data is available through EWGLI and identifies the country where the report of Legionnaires’ disease originates from.

Figure 6.5: Number of cases by country of report in Europe from 1987-2007

Number of cases by country of report in Europe from 1987-2007

It appears in Figure 6.5 that England and Wales have the highest number of cases of Legionnaires’ disease in Europe. This data must be interpreted with caution. Other countries may have very inaccurate and incomplete reporting systems and the numbers reflect the country where the report originates and not necessarily the country of source of disease i.e. does not differentiate travel associated sources from case that contracted the condition in England and Wales. Nearly half of the cases reported in England and Wales are thought to be contracted abroad, Figure 6.6.

Cases may be categorised into: community acquired, hospital acquired or travel associated. The majority of cases are thought to be sporadic although well-documented clusters have occurred in the UK in recent years, for example; Herefordshire and Barrow-in-Furness.

Nearly half (47.2%) of the cases occurring in residents from the West Midlands between 1994 and 2005 were associated with travel. Of these cases associated with travel the minority were travel within the UK (15.6%) but the majority abroad (84.4%).

Figure 6.6: Association between travel and reported cases of Legionnaires’ disease from Residents of the West Midlands 1994-2005

Association between travel and reported cases of Legionnaires’ disease from Residents of the West Midlands 1994-2005

The geographical spread of cases of Legionnaires’ disease in residents from the West Midlands is depicted in Table 6.2 showing the distribution by Health Protection Unit (HPU) of residence. It must be noted that the HPU of residence may not correspond to where the individual may have contracted the disease. The peak in Herefordshire in 2003 corresponds to a large single outbreak in that year  (RSU).

Table 6.2: Health Protection Unit of residence of patients with reported cases of Legionnaires’ disease in the West Midlands 1994-2005

Health Protection Unit of residence of patients with reported cases of Legionnaires’ disease in the West Midlands 1994-2005

References:

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2. Chin James. Control of Communicable Diseases Manual. Seventeenth Edition. American Public Health Association, Washington, 2000.
   
   
3. Centre for Disease Prevention and Control (CDC), general Legionnaires’ Disease information http://www.cdc.gov/ncidod/dbmd/diseaseinfo/legionellosis_t.htm, accessed 02.03.07
   
   
4. Centre for Disease Prevention and Control, information summary for the first defined Legionnaires’ disease outbreak in Philadelphia http://www.cdc.gov/mmwr/preview/mmwrhtml/00045731.htm, accessed 02.03.07.
   
   
5. European Working Group for Legionella Infections (EWGLI) http://www.ewgli.org/index.htm, accessed 22.02.07.
   
   
6. Health Protection Agency, (HPA), general Legionnaires’ Disease information. http://www.hpa.org.uk/infections/topics_az/legionella/menu.htm, accessed 02.03.07.
   
   
7. Health and Safety Executive UK, general Legionnaires’ Disease information. http://www.hse.gov.uk/legionnaires/index.htm, accessed 02.03.07
   
   
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10. West Midlands Regional Surveillance Unit (RSU), Health Protection Agency. West Midlands Legionnaires’ disease Surveillance, First Annual Report 2005.