Surveillance and disease data for Legionnaires' disease


  • Monitor the incidence of Legionnaires’ disease over time with respect to both community- acquired and travel-associated cases. 
  • Monitor the morbidity and mortality due to Legionnaires’ disease and attempt to identify particularly vulnerable populations. 
  • Provide relevant epidemiological and microbiological data to contribute to the development of recommendations on the control of outbreaks. 
  • Promote the development of a laboratory network for Legionnaires’ disease, including quality assurance and training. 
  • Support training for environmental microbiologists and public health experts in Legionnaires’ disease surveillance methods.


 Cases of Legionnaires’ disease are classified as confirmed or probable according to the EU surveillance case definition.

Surveillance of notified cases of Legionnaires’ disease

Once a year, EU Member States enter epidemiological data of Legionnaires’ disease cases that were notified in the previous year in the European Surveillance System (TESSy). ECDC then analyses the data to detect and monitor trends and to generate hypotheses for further research.

Surveillance of travel-associated Legionnaires’ disease

Cases of Legionnaires’ disease are defined as travel-associated if the patient stayed at or visited an accommodation site during the disease incubation period, i.e. two to ten days prior to symptom onset. Surveillance of a travel-associated Legionnaires’ disease is carried out on a day-to day basis to detect clusters, initiate preventive measures and to prevent subsequent cases. Each travel-associated case of Legionnaires’ disease diagnosed in the EU/EEA should be reported through TESSy as soon as possible. Cases of Legionnaires’ disease diagnosed in European citizens outside of EU Member States may also be reported to ECDC and trigger cluster identification in TESSy.

Follow-up of travel-associated clusters

A cluster of travel-associated cases of Legionnaires’ disease is defined as at least two cases being associated with the same accommodation site within two years (based on date of onset). Clusters of travel-associated Legionnaires’ disease are immediately notified by ELDSNet to all network members.
ELDSNet detects around 100 clusters of Legionnaires' disease cases each year at accommodation sites in Europe and beyond.
When a cluster is identified within an EU/EEA country, the public health authorities where the accommodation site is located are expected to report on the investigations done on the accommodation site. These reports should be submitted in a timely manner (by 2 and 6 weeks post-notification) and should show that adequate steps have been taken in order to control the risk of further Legionella infections at these sites in the future. If this timeline for reporting is not fulfilled or control measures stated are deemed unsatisfactory by ECDC, the name of the accommodation site is published on the ECDC website, in accordance with “Public disclosure of cluster/outbreak information” of Section 21 of the ELDSNet operating procedures. The name of the site will be removed only when a new report is received stating that adequate control measures have been implemented and steps have been taken to minimize the risk of further cases occurring.  All accommodation sites published are also notified to the International Federation of Tour Operators. If the country where the accommodation site is located is not an EU Member State, ELDSNet reports the cluster to the World Health Organisation (WHO) that is required to subsequently inform the Ministry of Health of the country concerned. ECDC welcomes any feedback on subsequent public health interventions, but does not publish any accommodation site names if such information is not received. All clusters outside the EU Member States, however, are notified to the International Federation of Tour Operators. Rapidly evolving clusters, defined as three cases with date of onset within a 3 months period (and at least one in the last 6 months) associated with the same accommodation site, are also notified to the International Federation of Tour Operators.

Laboratory activities

ELDSNet also funds reference laboratory activities, provided by the organisation awarded through an open call for tender. This call for tender is launched every fourth year. The work packages are:

  • Method standardisation and training. 
  • External quality assurance schemes for urinary antigen testing, detection of Legionella species in water, molecular typing of Legionella pneumophila, and detection by PCR. 
  • Support for investigations of travel-associated clusters of Legionnaires’ disease and of a limited number of community clusters. 
  • Scientific advice for ECDC.
  • Laboratory protocols which are available for ELDSNet members in the ELDSNet extranet workspace .


EU case definitions

List of case definitions for reporting communicable diseases to the Community network under Decision No 2119/98/EC of the European Parliament and of the Council.