KD Ricketts, B McNaught, CA Joseph
Health Protection Agency Centre for Infections, Respiratory Diseases
|Six hundred and fifty five cases of
travel-associated legionnaires’ disease with onset in 2004 have been
reported to the EWGLINET surveillance scheme by 25 countries. A total of
84.9% of cases were diagnosed by the urinary antigen test, and 37 cultures
were obtained. Thirty seven deaths were reported, giving a case fatality
rate of 5.6%.|
Eighty six new clusters were detected, 45% of which would not have been detected without the EWGLINET scheme. Ninety four accommodation sites were investigated and the names of four sites were published on the EWGLI website. Fifteen sites were associated with additional cases after a report was received to say that investigations and control measures had been satisfactorily carried out.
Further improvements could be made in the data collected on deaths due to travel-associated legionnaires’ disease, and on the number of samples taken for culture throughout Europe.
In 1976, an outbreak of a pneumonic illness at a hotel in Philadelphia in the United States led to the identification and recognition of legionnaires’ disease. By the late 1980s, it was clear that international collaboration would be required to facilitate exchange of information about this disease and to identify clusters of cases associated with individual accommodation sites. The European Working Group for Legionella Infections (EWGLI) was formed in 1986 and, in 1987, EWGLI established a surveillance scheme for travel-associated legionnaires’ disease (EWGLINET) that aims to track all cases of the disease in European travellers. When a cluster of cases is suspected to be associated with an accommodation site, EWGLINET initiates and monitors immediate control measures and investigations at the site, and ensures that international standards are adhered to. The history and current activities of EWGLI are described further on its website (http://www.ewgli.org/).
The number of cases reported to national surveillance schemes across Europe has been increasing. In 2004, 4588 cases were recorded in 35 countries  (including hospital-acquired and community-acquired cases, as well as travel-associated cases), compared with only 242 in 1993 from 19 countries. This increase in numbers can be attributed to an increasing awareness of the disease, a rise in the number of contributing countries, and strengthening of national and international surveillance systems. Of the total cases recorded in 2004, 396 (8.6%) died.
This paper provides results and commentary on cases of travel-associated legionnaires’ disease with onset in 2004 reported to EWGLINET.
Standard case definitions have been agreed by the collaborating countries in EWGLINET and are used for the purposes of international surveillance. A single case is defined as a person who, in the two to ten days before onset of illness, stayed at or visited an accommodation site that has not been associated with any other cases of legionnaires’ disease, or cases who stayed at an accommodation site linked to other cases of legionnaires’ disease but more than two years previously .
A cluster of travel associated legionnaires’ disease is defined as two or more cases in people who stayed at or visited the same accommodation site in the two to ten days before onset of illness and where onset is within the same two year period .
Cases are initially reported to their national surveillance schemes, which gather all relevant details on the case, such as information on microbiological diagnoses and travel history, and then report them to the EWGLINET coordinating centre at the Health Protection Agency Centre for Infections in London. There, the details are entered into a central database, which is then searched for other cases that stayed at the same accommodation sites as those visited by the new case. Either a single or a cluster notification will be faxed to collaborators, and the appropriate section of the EWGLINET investigation guidelines will be enacted.
In July 2002, European guidelines were introduced to standardise national responses to EWGLINET notifications . When collaborators are notified of a single case associated with (an) accommodation site(s) in their country, they are expected to issue a checklist to the site(s) to ensure that the risk of legionella infection is minimised. For cases associated with clusters, a more extensive response is required. Within two weeks the country of infection is expected to have returned a ‘Form A’ to the coordinating centre, stating that a risk assessment has been carried out and control measures are in progress. After a further four weeks (six weeks in total) the coordinating centre will expect to have received a ‘Form B’ stating that control measures and sampling have been carried out, giving the results of the sampling, and saying whether the accommodation site remains open or has been closed. If these forms are not received within the appropriate time periods, EWGLINET will publish the details of the site on its public website (http://www.ewgli.org/), stating that the coordinating centre cannot be confident that the accommodation site has adequate control measures in place. This notice is removed once the relevant form(s) have been received, confirming that measures to minimise the risk of legionella infection at the site have been taken.
The cases reported in 2004 generally fit the distinctive age and gender profile seen in previous years, with male cases outnumbering female cases by 2.9 to 1. The median age for male cases was 57 years (age range 23-96) and for female cases was 60 years (age range 29-84).
The usual pattern of a seasonal peak in summer was repeated in 2004, though with a single peak in August, rather than the July and September peaks witnessed in 2002 and 2003.
Thirty of the deaths were in men (81%), and seven in women (19%). All of the individuals who died were between 41 and 83 years old. Twenty five of the deaths were associated with single cases (68%), 12 with cluster cases (32%).
Of the 37 deaths in 2004, seven were diagnosed primarily by culture (19%), 27 primarily by urinary antigen (73%), two by serology (four-fold rise) (5%), and one by direct immunofluorescence (3%). Twenty two of the deaths were caused by ‘L. pneumophila serogroup 1’ infection (69.4%), one was due to ‘L. pneumophila other serogroup’ (2%), nine were attributed to ‘L. pneumophila serogroup unknown’, four to ‘Legionella unknown’ (11%), and one to ‘Legionella other species’ (3%) (the species was not specified).
The main category of organism detected in 2004 was ‘L. pneumophila serogroup 1’ (454 cases, 69.3%). The remaining cases were reported as ‘L. pneumophila other serogroup’ (13 cases, 2.0%), ‘L. pneumophila serogroup unknown’ (154 cases, 23.5%), ‘Legionella other species’ (2 cases, 0.3%), and ‘Legionella species unknown’ (32 cases, 4.9%).
Fifty five cases visited more than one European country, and ten cases
visited more than one country outside Europe. An additional 66 cases
(10.1%) visited countries outside the EWGLINET scheme.
In 2004, clusters were located in 24 countries, and one cluster was
associated with a cruise ship [TABLE 2]. Italy and France were associated
with the most clusters (17 clusters each, plus another cluster involving
sites in both Italy and Germany), followed by Spain and Turkey which were
each associated with nine clusters. Of the remaining clusters, the number
occurring in countries outside EWGLINET, or in EWGLINET countries not
officially signed up to follow the European guidelines, was 14
(representing 16%, an increase on the 13% seen in 2003, and following the
trend of increased cluster detection outside the area of operation of the
European guidelines). Five clusters involved two or more accommodation
sites, including the one mentioned above which spanned two countries
(Italy and Germany).
Most of the clusters in 2004 occurred during the summer months (66 between May and September, representing 77% of the full year figure). January was the only month in 2004 during which no clusters were detected.
Investigations and publications
In total, EWGLINET requested the investigation of 94 sites for clusters and cluster updates in 2004. Fifty three ‘Form B’ reports (56.4%) advised that samples from the accommodation site had tested positive for L. pneumophila (at concentrations equal to or greater than 1000 cfu/litre ), 38 (40.4%) reported that L. pneumophila was not detected in samples, and three ‘Form B’ reports (3.2%) did not have samples taken for reasons accepted by the coordinating centre.
The names of three French sites and one site in Turkey were published on the EWGLI website during 2004 for failure to return reports on time, or for failure to implement appropriate control measures in time. This represents a significant reduction from the 27 site names published during 2003.
During 2004, investigation reports were received for 149 sites associated with just a single case, even though the EWGLI guidelines do not require these. Of the 145 sites at which sampling was undertaken, 76 (52.4%) were reported positive for L. pneumophila.
The EWGLINET surveillance scheme for travel-associated legionnaires’ disease has now been in operation for 17 years. Each year the scheme detects a large number of clusters that involved no more than one case from any country and would otherwise have gone undetected. Thirty nine such clusters were identified by EWGLINET in 2004 (45%), and were therefore subjected to the high standard of investigation and control demanded by the EWGLI guidelines.
Italy and France continue to report a high proportion of their internal travel cases (for example, cases in French people travelling within France). These cases are important because they allow EWGLINET to detect additional clusters within Italy and France that might otherwise go undetected. EWGLINET encourages other countries to do the same by ensuring that their internal travel cases are reported.
The number of postings on the EWGLI website dropped dramatically in 2004, demonstrating that countries (especially Turkey, who had a much higher number of sites published in 2003 than in 2004) have adapted well to implementing the guidelines in a timely fashion. It is especially promising to note that the proportion of smaller clusters (clusters involving just two or three cases) has increased since the introduction of the EWGLI guidelines, which suggests that the standard of investigation and control outlined in the guidelines has proven sufficient to prevent a large number of further cases developing from those accommodation sites.
There continue to be areas where surveillance could be improved across Europe. Data on deaths is not as detailed as it could be. Cases are often reported to EWGLINET as ‘still ill’ or ‘unknown’, and these cases may eventually be fatal. Unfortunately, EWGLINET is rarely updated on the status of these cases, and after a year they become classified as ‘outcome unknown’. Collaborators are encouraged to let the coordinating centre know the outcome of cases that were reported while the patient was still ill. The proportion of cases reported to the scheme with known outcomes has been increasing, which is promising.
Cultures were taken for 19% of fatalities, which is an improvement on the cultures taken in only 5.6% of cases overall, but this percentage is still lower than would be liked. Fatal cases are often investigated more thoroughly than cases in patients who recover, and in order to demonstrate that the infection came from a particular source, a clinical culture is required for each case. Clinicians should be encouraged to take samples for culture wherever possible, and especially in fatal cases.
The seasonal pattern typically seen by EWGLI each year, with a concentration of cases during the summer months, can be explained for the most part by the fact that the scheme records only travel associated cases of legionnaires’ disease, and the majority of people in Europe choose to take their holidays during the northern hemisphere summer. However, national surveillance systems, which deal with community and hospital-acquired cases as well as travel-associated cases, also often see a marked increase in case numbers over the summer months that cannot be attributed solely to travel patterns. It may be that the warmer ambient temperatures in summer provide a more amenable environment for the legionella bacteria to multiply.
The surveillance scheme continues to expand to cover a greater number of European countries. The addition of Andorra to the scheme in 2004 brought the number of collaborating countries up to 37, but there are areas of eastern Europe that do not yet participate. It should be a priority for the scheme to form a working relationship with these countries with the intent of forming official collaborations with them at the earliest possible date, so that cases of travel-associated legionnaires’ disease occurring in their residents can be added to the European dataset.
* The list of EWGLI collaborators is available at the following URL address: http://www.eurosurveillance.org/em/v11n04/www.ewgli.org/contact/contact_listof_collaborators.asp
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