Causative Agent
The causative organism usually, Legionella pneumophila is a fastidious gram-negative rod. Fourteen serogroups are now recognised, as well around 40 other species of legionella, 14 of which have been shown to cause human cases of pneumonia. Cases are those which are clinically compatible and laboratory confirmed.
Clinical Description
Legionella, Legionellosis, Legionnaires' disease, Pontiac Fever.
Legionellosis is associated with two clinically and epidemiologically distinct illnesses: Legionnaires' disease, which is characterised by fever, myalgia, cough, pneumonia and Pontiac fever, a milder illness without pneumonia.
Transmission
Transmission is by inhalation of infected water droplets. Water systems
which maintain water temperatures of between 20 and 50°C are conducive
to the growth of Legionella, particularly where there are opportunities
for the formation of biofilm layers on surfaces. Cooling towers of air
conditioning systems, heat exchangers as well as supplies of potable
tap water and shower water can be prone to contamination and the organism
can survive in these environments for long periods.
Surveillance in Scotland
Legionnaires' disease is defined as "pneumonia due to infection with any Legionella species". Other illnesses associated with acute exposure are usually classified as Pontiac fever. Note: This distinction cannot be made with the main HPS database (DataEase) data. In 1994, SCIEH/HPS introduced an enhanced surveillance system for Legionella infections, which collects information on the clinical presentation and risk factors for each patient, in addition to detailed information on travel away from home during the incubation period of the illness (2-10 days).
Trends in Scotland (1995-2008)
In recent years the annual number of cases of L.pneumophila infection in Scotland has been relatively stable at around 20-50 cases per year, following a peak in the mid-80s. Additionally, there are usually up to four additional cases yearly due to other species except where these are the source of outbreaks. By far the largest source of infection is travel abroad, with cases associated with Scottish cooling towers accounting for less than 10% of the total.
Incidence and Risk
The incidence of Legionella in Scotland is low and is currently between 6 - 8 cases per 100,00 population per year, the majority of which are contracted overseas. Older age and male gender are both associated with increased risk, as is smoking [and underlying respiratory disease].
Prevention
Domestic hot water systems in large buildings appear, at least in Britain to be the most important source of endemic and epidemic Legionella infections.
The Health Protection Network has recently published new guidance:
There is also an HPS Guidance Note.
NHS Education for Scotland, in conjunction with the Health Protection Network have developed an online resource for the management of Legionella incidents and outbreaks in the community:
Cases of Legionellosis reported to HPS by age band, three year periods 1995-2006
Likely cases of Legionella infections reported to HPS, 2007-2008
Cases of Legionellosis reported by SLRL to HPS: 1995 to 2008
| Year |
Cases |
Male (%) |
Female (%) |
Deaths |
1995 |
38 |
32 (84.2 |
6 (15.8) |
3 |
1996 |
24 |
18 (75.0) |
6 25.0) |
4 |
1997 |
27 |
12 (44.4) |
15 (55.6) |
3 |
1998 |
44 |
34 (77.3) |
10 (22.7) |
3 |
1999 |
35 |
26 (74.3) |
9 (25.7) |
3 |
2000 |
32 |
22 (68.8) |
10 (31.3) |
3 |
2001 |
20 |
14 (70.0) |
6 (30.0) |
2 |
2002 |
36 |
24 (66.7) |
12 (33.3) |
2 |
2003 |
29 |
17 (58.6) |
12 (41.4) |
2 |
2004 |
32 |
23 (71.9 |
9 (28.1) |
4 |
2005 |
33 |
18 (54.5) |
15(45.5) |
1 |
2006 |
42 |
32 (76.2) |
10 (23.8) |
3 |
2007 |
43 |
28 (65.1) |
15 (34.9) |
1 |
2008 |
25 |
16 (64.0) |
9 (36.0) |
6 |
Annual Reports
Last reviewed: 22 October 2009
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