Legionnaires’ disease - Annual Epidemiological Report for 2015
In 2015, 30 countries reported 7 034 cases, 6 573 (93.4%) of which were classified as confirmed. The remaining 461 (6.6%) cases were reported as probable
• Legionnaires’ disease remains an uncommon, mainly sporadic respiratory infection with low notification rates in EU/EEA countries (overall 1.4 per 100 000 inhabitants).
• The overall notification rate has increased over the 2011−2015 period.
• Four countries (France, Germany, Italy and Spain) accounted for 69% of all notified cases in 2015.
• Regular checks for Legionella and appropriate control measures in man-made water systems may prevent a significant proportion of Legionnaires’ disease cases.
This surveillance report is based on Legionnaires’ disease (LD) surveillance data collected by the European Legionnaires’ Disease Surveillance Network (ELDSNet) for 2014. ELDSNet involves 30 EU/EEA Member States (28 EU Member States plus Iceland and Norway).
The surveillance data were collected through two different schemes:
1) Annual retrospective data collection of LD cases in EU Member States, Iceland and Norway.
2) Near-real-time reporting of travel-associated cases of Legionnaires’ disease (TALD), including reports from countries outside the EU/EEA. This scheme aims primarily at identifying clusters of cases that may otherwise not have been detected at the national level, which makes it possible to quickly investigate the reports and take control measures at the implicated accommodation sites to prevent further infections.
In 2015, the arrangements for surveillance of Legionnaires’ disease can be summarised as follows:
- Thirty EU/EEA Member States reported case-based LD data. Countries were asked to report cases in accordance with the 2012 EU/EEA case definition for confirmed cases or probable cases with at least one positive laboratory test for a probable case.
- Twenty-two EU/EEA countries and three non-EU/EEA countries reported TALD cases through real-time surveillance. TALD cases are defined as travellers having stayed at a commercial or public accommodation site in the two to ten days before onset of disease. This definition does not include cases of LD among travellers who stayed with relatives or friends. A single TALD case was defined as a person who stayed at an accommodation site not associated with LD cases in the previous two years. A TALD cluster was defined as two or more cases who stayed at the same accommodation site and whose dates of onset were within two years of each other.
A summary of national surveillance systems characteristics is available in the Annex.
In 2015, 30 countries reported 7 034 cases, 6 573 (93.4%) of which were classified as confirmed. The remaining 461 (6.6%) cases were reported as probable (Table 1). As in the previous year, the number of notifications per 100 000 inhabitants in 2015 was 1.4, which remains the highest number recorded. Age-standardised notification rates did not differ substantially from crude rates. Of 5 642 cases with known outcome, 456 were reported to have died, giving a case fatality of 8%.
L. pneumophila serogroup 1 was the most commonly identified pathogen, accounting for 679 of 834 (81%) culture-confirmed cases.
Four countries (France, Germany, Italy and Spain) accounted for 69% of all notified cases although their combined populations only represent approximately 50% of the EU/EEA population (Table 1 and Figure 1). Notification rates ranged from less than 0.1 per 100 000 inhabitants in Bulgaria, Poland and Romania to 5.1 per 100 000 in Slovenia (Table 1 and Figure 1).
As in previous years, most cases (69%) were community-acquired, while 21% were travel-associated, 8% were associated with healthcare facilities, and 2% were associated with other settings.
The distribution of cases by month of reporting peaked in August and September. Most cases (59%) had a date of onset between June and October (Figure 2).
The number of reported cases steadily increased over the 2011−2015 period (Figure 3).
In 2015, people aged 45 years and older accounted for 6 225 (89%) of 7 027 cases with known age. The notification rate increased with age, from ≤0.1 per 100 000 in those under 25 years of age to 3.5 in persons aged 65 years and above (5.4 per 100 000 in males and 2.0 in females) (Figure 4). The overall male-to-female ratio was 2.5:1.
Travel-associated Legionnaires’ disease
For 2015, 1 141 TALD cases were reported through the near-real-time surveillance scheme, 20% more than in 2014. A total of 167 new travel-associated clusters were detected in 33 countries, compared with 132 in 2014, 110 in 2013, and 99 in 2012. In 2015, 60% of the detected clusters of travel-associated Legionnaires’ disease were characterised by initial cases from several different countries. These clusters would probably not have been detected, had it not been for the international surveillance of ELDSNet.
Between 1 January and 31 December 2015, ECDC monitored eight threats in six countries and a European river cruise ship related to Legionnaires’ disease and involving 34 cases overall. All these threats were rapidly evolving clusters (≥3 cases with onset within three months).
In 2015, case numbers of LD in the EU/EEA were the highest ever observed, continuing the increase observed since 2011. The 2015 notification rate, although slightly higher, remains at the 2014 level of 1.4 notifications per 100 000 population. Contrary to 2014, no large outbreak contributed to the high number of reported cases. The main characteristics of the cases reported in 2015 were very similar to those reported in previous years: most cases were sporadic and community-acquired, and the disease mostly affected older males.
This increasing trend is probably driven by several factors including improved surveillance, an aging population, increasing travel, and climate change. Since the age-standardised notification rate also increased during the 2011−2015 period, demographic change can only partly explain the trend.
Climate change is expected to bring both an increase in heavy rainfall and higher temperatures. Such weather conditions are associated with higher LD incidence through a direct effect on the bacterial ecology and/or an increased use of potentially hazardous environmental sources such as air-conditioning systems with cooling towers .
Both 2014 and 2015 were the warmest years on record in Europe , although a direct causal association with the observed rates of LD remains to be demonstrated for these years.
Surveillance has certainly improved in Europe over the past decade as suggested by an evaluation carried out in France . Yet, many countries had a notification rate below 0.5, several even below 0.1 cases per 100 000, a situation unchanged over the past five years and unlikely to reflect the true incidence of LD in these countries.
Public health conclusions
Legionnaires’ disease remains an important cause of potentially preventable morbidity and mortality in Europe, and there is no indication of decreasing burden.
The priority for addressing the apparent gap in surveillance is to assist countries with notification rates below 0.1 per 100 000 inhabitants in improving both the diagnosis and the reporting of Legionnaires’ disease.
Regular checks for the presence of Legionella bacteria and appropriate control measures applied to man-made water systems may prevent cases of Legionnaires’ disease at tourist accommodation sites, in hospitals, in long-term healthcare facilities or other settings where sizeable populations at higher risk may be exposed .
- Sakamoto R. Legionnaire’s disease, weather and climate. Bull World Health Organ. 2015 Mar; 93: 435–436.
- European Reanalysis and Observations for Monitoring. 2015: joint warmest year on record in Europe, EURO4M Climate Indicator Bulletin. 2016 Jan 25. Available from: http://cib.knmi.nl/mediawiki/index.php/2015:_joint_warmest_year_on_record_in_Europe
- Campese C, Jarraud S, Sommen C, Maine C, Che D. Legionnaires’ disease in France: sensitivity of the mandatory notification has improved over the last decade. Epidemiol Infect. 2013 Mar;141(12): 2644-2649
- Bartram J, Chartier Y, Lee JV, Pond K, Surman-Lee S (editors). Legionella and the prevention of legionellosis. Geneva: World Health Organization, 2007. Available from: http://www.who.int/water_sanitation_health/emerging/legionella.pdf
European Centre for Disease Prevention and Control. Legionnaires’ disease surveillance in Europe, 2009. Stockholm: ECDC; 2011. Available from: http://ecdc.europa.eu/en/publications-data/surveillance-report-legionnaires-disease-europe-2009
European Centre for Disease Prevention and Control. Legionnaires’ disease surveillance in Europe, 2010. Stockholm: ECDC; 2012. Available from: http://www.ecdc.europa.eu/en/publications-data/legionnaires-disease-europe-2010
European Centre for Disease Prevention and Control. Legionnaires’ disease surveillance in Europe, 2011. Stockholm: ECDC; 2013. Available from: http://ecdc.europa.eu/en/publications/Publications/legionnaires-disease-in-europe-2011
European Centre for Disease Prevention and Control. Legionnaires’ disease surveillance in Europe, 2012. Stockholm: ECDC; 2014. Available from: http://ecdc.europa.eu/en/publications-data/legionnaires-disease-europe-2011
European Centre for Disease Prevention and Control. Legionnaires’ disease surveillance in Europe, 2013. Stockholm: ECDC; 2015. Available from: http://ecdc.europa.eu/en/publications-data/legionnaires-disease-europe-2013
European Centre for Disease Prevention and Control. Legionnaires’ disease surveillance in Europe, 2014. Stockholm: ECDC; 2016. Available from: http://ecdc.europa.eu/en/publications-data/legionnaires-disease-europe-2014
Peer-reviewed articles by ECDC epidemiologists
Beauté J, Sandin S, Uldum SA, Rota MC, Brandsema P, Giesecke J, et al. Short-term effects of atmospheric pressure, temperature, and rainfall on notification rate of community-acquired Legionnaires’ disease in four European countries. Epidemiol Infect. 2016 Aug 30:1-11.
De Jong B, Payne Hallström L, Robesyn E, Ursut D, Zucs P, European Legionnaires’ Disease Surveillance Network. Travel-associated Legionnaires’ disease in Europe, 2010. Euro Surveill. 2013;18(23).
Beauté J, Zucs P, de Jong B, European Legionnaires’ Disease Surveillance Network. Legionnaires’ disease in Europe, 2009–2010. Euro Surveill. 2013;18(10):20417.
Beauté J, Zucs P, de Jong B. Risk for travel-associated Legionnaires’ disease, Europe, 2009. Emerging Infect Dis. 2012 Nov;18(11):1811–6.
* The European Surveillance System (TESSy) is a system for the collection, analysis and dissemination of data on communicable diseases. EU Member States and EEA countries contribute to the system by uploading their infectious disease surveillance data at regular intervals.
Figure 1. Rate of confirmed Legionnaires’ disease cases per 100 000 population by country, EU/EEA, 2015
Rate of confirmed Legionnaires’ disease cases per 100 000 population by country, EU/EEA, 2015