There are two clinically and epidemiologically distinct forms of legionellosis:
Legionnaires' disease - uncommon, potentially fatal form of pneumonia,
characterised by fever, myalgia and cough).
Pontiac Fever - milder flu-like illness without pneumonia.
- Majority of cases in Europe are caused by Legionella pneumophila.
- There are sixteen serogroups of Legionella pneumophila, the most common
is serogroup 1.
- In addition there are over 50 other species of Legionella bacteria that
have been shown to cause human disease.
Source and route of exposure
Legionella bacteria are widely distributed in natural and artificial water supplies and in soil. They grow best in stagnant, warm water (24-45 °C) and are associated with bio-film and amoebae.
In addition, Legionella longbeachae is associated with growing media (potting compost) and has not been identified in water supplies. Legionnaires' disease caused by Legionella longbeachae is very uncommon.
Exposure is airborne (either indoor or outdoor) usually through aerosolised water containing the bacteria. Equipment capable of producing aerosols and which have most often been implicated in outbreaks, are:
- cooling towers (often used for controlling the temperature of industrial processes);
- air conditioning systems cooled by water;
- whirlpool spas.
Good quality maintenance of these is essential to prevent legionella growth.
The bacteria are not transmissible from person to person.
Infection is by inhalation of aerosols containing the bacteria emitted from a source with significant legionella growth.
The incubation period for Legionnaires' disease is 2-10 days, most commonly 5-6 days.
The incubation period for Pontiac Fever is 0-3 days, mostly commonly 1-2 days.
Surveillance in Scotland
Health Protection Scotland undertakes surveillance of legionellosis in Scotland,
working closely with the Scottish Haemophilus,
Legionella, Meningococcus and Pneumococcus Reference Laboratory at Stobhill
As there are many causes of pneumonia and flu-like illness, only laboratory confirmed
cases of legionellosis are subject to enhanced surveillance.
Enhanced surveillance involves follow up by the Health Protection Team of the NHS
board with the resident case. Information sought includes:
clinical presentation of disease;
possible exposures in the 10 days before illness;
detailed information of travel away from home in the 10 days before illness.
Travel-related Legionnaires’ disease
In addition, Scotland participates in the Europe-wide travel-related Legionnaires'
disease surveillance scheme (ELDSNet). All travel-related Legionnaires' disease
cases are reported to ELDSNet as soon as possible, so that outbreaks can be identified
as quickly as possible, the source of infection identified and appropriate action
See ELDSNet page on ECDC website.
Trends in Scotland (2000-2012)
In the period 2000-2012, there have generally been between 20-45 cases of Legionnaires' disease diagnosed in Scotland and reported to HPS per year. This includes travellers to Scotland who may fall ill whilst here, Scottish travellers who may be exposed abroad and become ill when they return, community acquired cases and hospital-acquired cases. This count does not include Scottish travellers who become ill and are treated abroad. Over this time, 8.3% of reported cases have died from their infection or complications arising from their infection, see Table 1 below. An unexpectedly high number of cases was seen in 2012 due to an outbreak of Legionnaires’ disease in south-west Edinburgh, which included 56 laboratory-confirmed cases.
Cases are more likely to be male – on average 66.5% of cases. Cases are more likely to be older, with the most common age group as 60-69 years old. Cases in those aged under 40 years are uncommon, see Figure 1.
Table 1: Cases of Legionnaires' disease diagnosed in Scotland reported by to HPS: 2000-2012
|| 22 (69)
|| 10 (31)
|| 3 (9)
|| 14 (70)
|| 6 (30)
|| 2 (10)
|| 24 (67)
|| 12 (33)
|| 2 (6)
|| 17 (59)
|| 12 (41)
|| 2 (7)
|| 23 (72)
|| 9 (28)
|| 4 (12)
|| 18 (55)
|| 15 (45)
|| 1 (3)
|| 32 (76)
|| 10 (24)
|| 3 (7)
|| 28 (65)
|| 15 (35)
|| 1 (2)
|| 16 (64)
|| 9 (36)
|| 6 (24)
|| 17 (68)
|| 8 (32)
|| 3 (12)
|| 8 (50)
|| 8 (50)
|| 0 (0)
|| 23 (72)
|| 9 (28)
|| 6 (19)
Figure 1: Age distribution of
Scottish cases of legionnaires' disease 2000-2012
Cases are more likely to be travel-related, accounting for around 60% of cases between 2000 and 2012 (see Figure 2). Community acquired Legionnaires' disease has accounted for around 40% of cases between 2000 and 2012.
Figure 2: Sources of Legionnaires'
disease for Scottish cases 2000-2012
Cases are predominantly Legionella pneumophila serogroup 1, with 70% of
cases diagnosed in 1995-2010 as Legionella pneumophila serogroup 1.
Incidence and Risk
The incidence of Legionella in Scotland is low and is currently 6 - 8 cases per 100,000 population per year, in years when there is no large community outbreak.
Smoking and underlying respiratory disease are both associated with increased risk.
The Health Protection Network has produced guidance on the management of Legionella
incidents, outbreaks and clusters in the community.
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.
HPS publishes a detailed analysis of Legionniares’ disease cases in Scotland every two years. The last report, released in August 2013, provided an analysis of data from 2011 and 2012.
Legionella longbeachae cluster
In August - September 2013 there was a cluster of seven cases of Legionnaires’ disease caused by Legionella longbeachae. This was investigated by a national IMT led by HPS. A report detailing this investigation is available.
In September 2013 HPS investigated further cases of Legionella longbeachae. See HPS Weekly Report - 18 September 2013.
As part of the management of these cases the following gardening good hygiene advice has been prepared:
|Gardening Good Hygiene
A few simple good hygiene tips can help you during gardening:
- wear gloves;
- wear a dust mask if you are working on anything dusty, particularly indoors;
- wash your hands as soon as you finish;
- if you are going to smoke, wash your hands before doing so.
|Storing and Handling Compost, Potting Mix, Mulches and Soil
As well as the general advice above, the following advice can help you avoid breathing in dust:
- store compost, potting mixes, mulches and soil in a cool place, away from the sun;
- open any bags carefully in a well ventilated area and if possible using a safety blade or sharp knife;
- keep the door or a window open in greenhouses or sheds when potting-up plants or filling hanging baskets;
- wear a dust mask if you are working on anything dusty, particularly indoors.
In 2012 HPS undertook an investigation into cases of Legionella longbeachae in Scotland between 2008 and 2012. This is an unusual form of Legionella and is associated with growing media (or potting compost). In the period 2008-2012 there were nine cases of Legionella longbeachae, whereas in the rest of the UK there was one case. The investigation considered why Scotland should have an unusually high number of cases and investigated commercial growing media production for Scotland. The investigation concluded that the difference in case ascertainment was probably due to a more pro-active investigation of cases in Scotland. No differences in growing media production for Scotland compared with the rest of the UK could be identified.
Legionnaire's disease- South West Edinburgh 2012
In May/June 2012 there was an outbreak of Legionnaires’ disease in south-west Edinburgh. This outbreak involved 56 confirmed cases of Legionnaires’ disease. This outbreak was managed by NHS Lothian and they have published an interim report on this outbreak.
Other Sources of Information
For basic information about legionellosis and symptoms, see the
NHS Inform web pages on Legionnaires' disease
ECDC web pages on legionellosis
Public Health England (formerly HPA) web pages on Legionnaires' disease
Last reviewed: 19 September 2013