:: Home > Archives
: Eurosurveillance
monthly releases 2007 > Volume
12 / Issue 12

[ previous page
]

Euroroundup

Legionnaires’ disease in
Europe: 2005-2006

volume

12

issue

12

publication date

December 2007

How to cite this
article, click
here.

Indexed in MedLine
as: Euro Surveill 2007;12(12)[Epub ahead of
print]

Published online December
2007

Key words:
Legionella. Legionellosis. Europe.

Legionnaires’ disease in Europe:
2005-2006

KD Ricketts ([email-masked]),
CA Joseph on behalf of the European Working Group for Legionella
Infections (EWGLI)

Health Protection Agency Centre for Infections. Respiratory Diseases
Department, London, UK

Once a year, every country that participates in the European
Surveillance Scheme for Travel Associated Legionnaires’ Disease (EWGLINET)
is asked to submit a dataset comprising all cases of Legionnaires’ disease
(not only travel-associated) with date of onset in the previous year. This
paper presents the data collected for 2005 and 2006.
In this period,
11,980 cases were reported by 35 countries, showing a continued increase
compared with earlier years. 214 outbreaks or clusters were reported,
involving 1028 cases. 377 cases died, giving a case fatality rate of 6.6%.
The highest incidence rates in both years were recorded in Spain, while
six countries reported a rate of less than one case per million population
in at least one of the years. Incidence rates by age group were included
in the dataset for the first time, showing an increase of the overall rate
with age.
Main method of diagnosis was the urinary antigen test
(76.0%), whilst the percentage of cases diagnosed by culture fell from
10.0% in previous years to 8.9% in 2005-2006.

Introduction

Legionnaires’ disease is an atypical pneumonic illness
caused by the Legionella bacteria. These bacteria can be found
naturally in environmental water sources such as rivers, lakes and
reservoirs, usually in low numbers. The organism favours warm, stagnant
waters, and becomes infective when aerosolised. Poorly maintained
aerosol-generating devices can act as a source of the disease, and have
been responsible for outbreaks affecting up to 400 cases [1]. Wet cooling
systems, water systems and spa pools are all well documented sources of
Legionnaires’ disease [1].

The identification of Legionnaires’ disease in 1977 led to the
establishment of the European Working Group for Legionella Infections
(EWGLI) in 1986. The group aimed to share knowledge and to monitor trends
in legionella infections across Europe. Currently, 35 countries are
members of EWGLI.

Every year the EWGLI participating countries are asked to submit data
on the cases of Legionnaires’ disease that have been diagnosed in their
residents during the preceding year to the co-ordinating centre in London.
This allows for analysis of this disease on a European level and for
comparison of trends between countries. Data from the years 1996 to 2004
have been published previously [2-7]. This paper presents the dataset for
the years 2005-2006.

Methods

Participating countries submit an aggregated
epidemiological and microbiological dataset using standardised reporting
forms. The following data is collected: the number of confirmed and
presumptive cases diagnosed in the reporting country during the preceding
year, how many died, and the population base covered by the reporters; the
method of diagnosis and the species and serogroup of any isolates
obtained; age group and sex of the cases (age standardised rates were
introduced into the dataset for the first time in 2005); category of
exposure (nosocomial [hospital-acquired], travel or community); countries
of travel for the travel-associated cases; outbreaks by type, size and
suspected source.

Cases are classified as confirmed or presumptive, based upon the EWGLI
case definitions [8]. If the method of diagnosis is not known, the case is
classified as ‘diagnosis not known’.

Each case is further categorised by exposure history into ‘travel’,
‘nosocomial’ and ‘community’ cases. This is determined for each case by
the country of report according to national definitions. In instances
where there is insufficient evidence to allocate a case to one of the
existing categories (e.g. cases that spent part of their incubation period
both in hospital and travelling), the case is categorised as ‘other’, and
if there is no exposure information available, the case is allocated to
the ‘not known’ category.

Where incidence rates per million population are calculated, they are
based upon the reported population size. Regional rather than national
incidence rates were obtained for six countries in 2005 (Bulgaria,
Croatia, Czech Republic, Lithuania, Romania, Russia) and four in 2006
(Bulgaria, Lithuania, Russia, Romania), and it should be noted that these
data may not be representative of the entire country.

In this report, the term ‘outbreak’ is used to describe outbreaks in
hospitals or community settings, whereas the term ‘cluster’ is used to
describe this type of incident when associated with hotels or other
tourist accommodation sites. Every country defines its outbreaks
independently, whilst clusters are defined as ‘two cases associated with
the same accommodation site within two years’, based upon EWGLINET’s
definition.

Results

In 1993, only 19 countries reported a dataset to EWGLI.
The response rate has risen significantly since then to 35 countries in
both 2005 and 2006. The number of cases reported was 5,700 in 2005 and
6,280 in 2006. In the fourteen years for which this dataset has been
collected, 41,627 cases have been reported (Table 1). [Note that in
previous publications, the number of cases for 1993 was erroneously
reported as 242 instead of 1,242]

Incidence per million population
In both
years the highest incidence rates were reported by Spain (28.4/1,000,000
population in 2005 and 30.0/1,000,000 in 2006), followed in 2005 by France
(24.8/1,000,000 in 2005 and 23.0/1,000,000 in 2006) and in 2006 by the
Netherlands (16.7/1,000,000 in 2005 and 26.9/1,000,000 in 2006). Five
countries reported incidences of less than one case per million population
in 2005 (Latvia, Malta, Poland, Slovakia and Turkey), in comparison with
four countries in 2006 (Latvia, Romania, Slovakia and Turkey). Table 2
shows rates of Legionnaires’ disease per million population for 10
countries, selection based upon their consistent rates, and in order to
allow comparison with previous papers.

The overall incidence for Europe was 10.3/1,000,000 in 2005 (based on a
denominator population of 550.8 million) and 11.2/1,000,000 in 2006 (based
on a denominator of 562.7 million) (Table 1).

Category of cases
For the two years
2005-2006, 629 cases were reported as nosocomial, 7,041 as community
cases, 1,395 as associated with travel abroad, 1,227 as associated with
travel within the country of residence, 126 as ‘other’ and 1,562 as ‘not
known’ category of infection (Table 3).

Age of cases
A breakdown of cases by age
group was available in both years for all countries except Czech Republic,
Former Yugoslav Republic of Macedonia, Germany, Iceland, Israel and
Portugal. National demographic data on population size by age group were
also provided in order to calculate age standardised rates.
The peak
age group of cases was 50-59 in both years; 1,164 cases in this age group
were reported in 2005 and 1,289 cases in 2006. Whilst in both years the
number of reported cases in the older age groups decreased with age (60-69
years: 1,076 in 2005, 1,170 in 2006; 70-79 years: 914 in 2005, 1,026 in
2006; 80+ years: 639 in 2005, 726 in 2006), the overall age standardised
incidence rates increased with increasing age (60-69 years: 2.6 cases per
100,000 in 2005, 2.86 in 2006; 70-79 years: 2.91 in 2005, 3.32 in 2006;
80+ years: 3.83 in 2005, 4.32 in 2006). This increase in incidence rate
with age was seen for some individual countries (e.g. France, Italy), but
did not hold for all (e.g. England and Wales, The Netherlands) (Table 4).

Outbreaks
During the two years, there
were a total of 214 outbreaks or clusters, detected by 18 countries and
involving 1,028 cases, 8.6% of the total dataset (Table 5). Countries
reported 408 cases associated with 107 outbreaks in 2005, and 620 cases
associated with 107 outbreaks in 2006. The outbreaks ranged in size from
two to 146 cases. The largest outbreaks in both years occurred in Spain
and were attributed to wet cooling systems; involving 50 cases in 2005 [9]
and 146 in 2006 [10]. The number of deaths associated with these outbreaks
could not be determined from the information collected in this dataset.

Nineteen outbreaks (8.9%) involving 66 cases were linked to hospitals
or healthcare facilities and occurred in Austria, Denmark, England and
Wales, France, Germany, Ireland, The Netherlands, Poland, Portugal and
Spain. Fifteen of these were attributed to contaminated hot or cold water
systems, two to wet cooling systems, and two to an unknown source. These
sources are as reported by collaborators, and the standard of
investigation may vary between countries.

Forty-four outbreaks (20.6%) were linked to community settings, and
involved 522 cases. They occurred in Austria, England and Wales, France,
Germany, The Netherlands, Northern Ireland, Poland, Portugal, Scotland and
Spain. Wet cooling systems were identified as the source in 19 outbreaks,
five were attributed to hot or cold water systems, four to whirlpool spas,
15 to an unknown source and one to the sediment at the base of a
pressurised water tank [11].

One hundred and forty-three clusters (66.8%) were associated with
travel; 94 (44%) with travel outside the country of residence, and 49
(23%) with travel within the country of residence. Hot or cold water
systems were responsible for 52 of the clusters, a wet cooling system in
one cluster, and whirlpool spas in three. No source was identified for the
remaining clusters.

Two outbreaks (one in each year) were linked to prisons, and in both
the source of infection was identified as the hot or cold water system.
One 2006 outbreak was associated with a nursing home, for which the source
was not identified, and the remaining five outbreaks (one in 2005, the
rest in 2006) were associated with private homes or buildings. In two of
these latter outbreaks, the hot water systems were identified as the
source; for the remaining three no source was identified.

Travel-related legionella infection

Altogether in 2005-2006, 26 countries reported a total of 2,622
travel-associated cases; 1,395 were classified as ‘travel abroad’ and
1,227 were associated with travel in the patient’s country of residence
(Table 3). Nine countries in 2005 and five countries in 2006 reported no
travel-associated cases. Travel within Europe accounted for 89.2% of the
travel-associated cases in 2005 (1142 cases) and 90.0% in 2006 (1208
cases). Travel on cruise ships was associated with two cases in 2005 and
11 in 2006.

Spain was associated with the most travel-related cases over this
two-year period (545 cases), followed by France (497 cases) and Italy (450
cases). These countries may be disproportionately represented as countries
of infection because they reported the highest number of cases in general,
and the majority of the travel-associated cases in these countries (59.6%,
77.3% and 53.3%) occurred as a result of domestic travel.

A more detailed analysis of travel-associated cases of Legionnaires’
disease is published each year from EWGLI’s surveillance scheme (EWGLINET)
[12]. EWGLINET operates a strict case definition for travel-associated
infections, and so not all cases reported as travel in this dataset are
reported to the EWGLINET travel dataset. EWGLINET’s case definition
excludes patients who had stayed in private accommodation, patients for
whom travel information was incomplete, or those for whom travel did not
fall within the strict 2-10 day incubation period. EWGLINET does not
include these cases because it would not be possible to investigate them
further or to link them to other cases who shared the same accommodation
site.

Main method of diagnosis
EWGLI
collaborators allocate a main method of diagnosis to each reported case,
taking culture as the ‘gold-standard’ test. The majority of cases in 2005
and 2006 were primarily diagnosed by urinary antigen detection (9,100
cases, 76.0%), followed by isolation/culture for 1,067 cases (8.9%),
single high antibody titres in 716 cases (6.0%), and a fourfold rise in
antibody detection levels for 274 cases (2.3%). The remaining cases were
diagnosed by respiratory antigen detection, PCR, other methods or the
method was unknown (Table 6).

In 2006 compared with 2005, the percentage of cases diagnosed primarily
by culture fell from 9.3% to 8.6%, whilst the number of cases with urinary
antigen detection as the main method of diagnosis increased from 71.3% to
80.2%. The proportion of cases diagnosed serologically (including both
seroconversions and single high titres) fell from 8.8% to 7.8%.

‘Legionella pneumophila serogroup 1’ accounted for 9,219 cases
(77.0%) over the two years, ‘L. pneumophila other serogroup or
serogroup not determined’ accounted for 1,862 cases (15.5%), and 899
(7.5%) were reported as ‘other Legionella species’ or ‘species
not known’.

Of the 1,067 isolates obtained, 862 (80.8%) were identified as L.
pneumophila serogroup 1, 94 (8.8%) were L. pneumophila
serogroups 2-16 and 74 (6.9%) were L. pneumophila serogroup
unknown. Seventeen isolates were diagnosed as other species of
Legionella. These were reported as L. anisa (1), L.
bozemanii (2), L. brunensis (1), L. cincinnatiensis
(1), L. feeleii (1), L. jordanis (1), L.
longbeachae (4), and L. micdadei (6). For 20 isolates, the
Legionella species was not known.

Deaths
There were 377 deaths reported in
2005 (case fatality rate of 6.6%) compared with 387 deaths in 2006 (case
fatality rate of 6.2%). In some countries it is not compulsory to report
deaths, and so these figures may underestimate the true mortality
attributable to Legionnaires’ disease.

Discussion

The number of cases reported each year to the scheme
continues to increase. This rise in case numbers can be partly attributed
to increasing ascertainment as national surveillance schemes strengthen.
It is especially notable that awareness of Legionnaires’ disease is rising
in the newer European Union member states. Invitation to submit annual
datasets of cases each year appears to be helping in raising the profile
of the disease in these countries, whereas comparison of the rates between
countries can highlight the extent of the under-ascertainment. EWGLI hopes
that the number of cases reported by these countries in the future annual
datasets will increase to better reflect the true number of cases.

Every year, the number of nosocomial cases reported to the dataset
remains relatively static (between 300 and 350 since 2003 [7]). In the
context of increasing overall case numbers this stability is an
encouraging trend, especially since case fatality rates are higher amongst
nosocomial cases than amongst other categories [13]. Also, the number of
large community outbreaks has been decreasing in recent years. Community
outbreaks are unpredictable, so it is difficult to determine whether this
decrease is real or artifactual. However, more extensive legislation has
been introduced across Europe in recent years for the control and
prevention of Legionnaires’ disease, which is probably having a beneficial
effect [14-16]. Authorities should be encouraged to ensure that national
or WHO guidelines are being utilised in national health care systems [1].

EWGLI has repeatedly raised the problems associated with a decrease in
the number of clinical isolates being obtained but, despite this, the
number fell again during 2005-2006 to 8.9% (in comparison with 10.0% in
2003-2004 [6]). Lack of clinical isolates can cause difficulties for
public health authorities when investigating clusters; with no clinical
isolate to compare with any environmental isolates obtained, the suspected
source of the outbreak cannot be microbiologically confirmed. As
Legionella is a relatively ubiquitous organism in the environment,
microbiological confirmation is an important step in determining the
source of infection. As the urinary antigen test becomes ever more
widespread, this problem is likely to become exacerbated. The increasing
use of the urinary antigen test probably also accounts for the high
proportion of L. pneumophila serogroup 1 reported to EWGLI, since
the test almost exclusively detects these organisms.

The overall incidence rates recorded in this dataset show an increasing
rate with increasing age. This is a new variable collected in the dataset
and the resulting figures have important implications for Europe’s aging
population. Countries should expect an increase of case numbers and a
greater demand for health services due to Legionnaires’ disease in the
future. There are some countries that do not show this increasing rate
with age, however, it is difficult to determine whether this is due to
different testing policies or to true trends in the incidence rates.

In 2010, EWGLINET and the collection of this annual dataset will
transfer to the European Centre for Disease Prevention and Control (ECDC).
This annual dataset has now been collected for fourteen years, to comprise
the largest dataset of cases of Legionnaires’ disease in the world and
should be continued. EWGLINET itself has been a valuable tool in raising
awareness of the disease among members and national surveillance
structures, and has contributed to the introduction of regulations and
guidelines across Europe. This type of European surveillance is especially
important for preventable diseases with environmental sources, as prompt
action can tackle these sources as they emerge. With the ageing of
populations across Europe, and therefore more people at risk from
Legionnaires’ disease, EWGLINET’s importance will only increase.

EWGLI hopes that the ECDC will encourage countries, especially the new
EU Member States, to develop their national surveillance schemes and
submit their annual data so that surveillance of the Legionnaires’ disease
across Europe can continue unabated.

Acknowledgements

EWGLI is partially funded by the European Centre for
Disease Prevention and Control. We would like to thank our collaborators
for completing their annual datasets and Mrs Rekha Yadav for collecting
the data.

References

World Health Organisation. Legionella and the prevention of
legionellosis. Eds: Bartram J, Chartier Y, Lee JV, Pond K, Surman-Lee S
(2006).

Anonymous. Legionnaires’ disease in Europe, 1996. Wkly Epidemiol
Rec. 1997; 72:253-260.

Anonymous. Legionnaires’ disease in Europe, 1997. Wkly Epidemiol
Rec. 1998; 73:257-264.

Anonymous. Legionnaires’ disease in Europe, 1998. Wkly Epidemiol
Rec. 1999; 74:273-280.

Anonymous. Legionnaires’ disease in Europe, 1999. Wkly Epidemiol
Rec. 2000; 75:347-352.

Joseph CA. Legionnaires’ disease in Europe 2000-2002. Epidemiol.
Infect. 2004;(132):417-424.

Ricketts K, Joseph C, . Legionnaires' disease in Europe 2003-2004.
Euro Surveill 2005;10(12):256-9. Available online: http://www.eurosurveillance.org/em/v10n12/1012-226.asp

EWGLI. Case definitions. Available online: http://www.ewgli.org/ewglinet/case_definitions.htm
(Accessed 15th June 2007)

Sala M, Arias C, Oliva J, Pedrol A, Roura P, Domínguez A, .
Community outbreak of Legionnaires’ disease in Vic-Gurb, Spain in
October and November 2005. Euro Surveill 2007;12(3)[Epub ahead of
print]. Available online: http://www.eurosurveillance.org/em/v12n03/1203-223.asp

Castilla J, Barricarte A, Aldaz J, Garcia Cenoz M, Ferrer T, Pelaz
C, Pineda S, et al.. A large Legionnaires' disease outbreak in Pamplona,
Spain: early detection, rapid control and no case fatality. Epidemiol
Infect. 2007 Jul 30;:1-10 [Epub ahead of print]

Anon. Legionella cases, Fochabers Health Protection Scotland,
E-Weekly Report 2005. Vol 39(39). http://www.hps.scot.nhs.uk/ewr/article.aspx
(Last accessed 07.11.07).

Ricketts K, McNaught B, Joseph C, European Working Group for
Legionella Infections, . Travel-associated legionnaires’ disease in
Europe: 2005. Euro Surveill 2007;12(1)[Epub ahead of print]. Available
online: http://www.eurosurveillance.org/em/v12n01/1201-228.asp

Pedro-Botet ML, Mateu L, Sopena N, Roure S, Casas I, Garcia-Nunez M,
Rey-Joly C, Sabria M. Hospital- and Community-acquired Legionella
pneumonia: two faces of the same disease? In Cianciotto NP et al.
Legionella: State of the art 30 years after its recognition.

Isakbaeva E, Blystad H. New legislation in Norway targets prevention
of legionnaires’ disease. Euro Surveill 2005;10(7):E050714.2. Available
from: http://www.eurosurveillance.org/ew/2005/050714.asp#2

Kontrolle und Prävention der Reise-Assoziierten Legionärskrankheit.
AGES – Osterreichische Agentur fur Gesundheit und Ernahrungssicherheit
(2005).

Public Health Act, 2003 (Act No. XIII of 2003). Control of
Legionella Regulations, 2006. Malta (2006).

Citation
style for this article: Ricketts K, Joseph C, .
Legionnaires’ disease in Europe: 2005-2006. Euro Surveill 2007;12(12)[Epub ahead
of print]. Available online:
http://www.eurosurveillance.org/em/v12n12/1212-224.asp

The opinions expressed by authors
contributing to Eurosurveillance do not necessarily reflect the
opinions of the European Centre for Disease Prevention and Control
(ECDC) or the Editorial team or the institutions with which the
authors are affiliated. Neither the ECDC nor any person acting on
behalf of the ECDC is responsible for the use which might be made of
the information in this journal.

Eurosurveillance [ISSN] - ©2007 All rights
reserved.