European Surveillance of Legionnaires' Disease

Legionnaires' disease and Pontiac fever are both diseases with important public health implications and require prompt and thorough responses to outbreaks for future prevention. Effective methods for defining, diagnosing, reporting and responding to legionellosis outbreaks ideally should be standardized across countries. Therefore, the European Union surveillance methods for countering Legionnaires' disease is a useful model especially for travel-associated Legionnaires' disease (TALD) cases which are on the rise. Multi-country surveillance in the EU and European Economic Area (EEA) has evolved since the first organizational efforts in the 1980's to the currently responsible, European Legionnaires' Disease Surveillance Network (ELDSNet). This chapter outlines the practices of the EU surveillance of Legionnaires' disease including their schemata, definitions, responsibilities of participating members, methods and the results of the data collected since the program's inception. Lastly, improvements must still be made as the incidence of Legionnaires' Curr. Issues Mol. Biol. 42: 81-96. caister.com/cimb caister.com/cimb 81 Curr. Issues Mol. Biol. Vol. 42 Curr. Issues Mol. Biol. 42: 81-96. caister.com/cimb


Introduction
Legionnaires' disease is a statutorily notifiable disease in all EU and EEA countries. However, the case definitions across different countries varies.
In some countries legionellosis, in general, is a notifiable disease which includes cases of both Legionnaires' disease and Pontiac fever. However, in other countries only Legionnaires' disease is a notifiable disease. There are also discrepancies between countries in the laboratory methods used.
A case definition that includes both epidemiological and microbiological criteria is therefore essential when performing surveillance. Such a definition should accomplish the following: • Set standards for defining cases; • Compare data between countries; • Verify the diagnosis and share laboratory results; • Facilitate international investigations and collaborations; • Develop best practice within and between countries.
For EU surveillance, a case definition for Legionnaires

EU Surveillance
The surveillance data are from two different schemes: the first scheme covers all cases reported annually from EU Member States and EEA countries with the following objectives: disease.

Data collection methods
The collection of national data covering all reported cases annually is

Single case
Case of Legionnaires' disease who in the two to ten days before onset of illness stayed at or visited a commercial accommodation site that has not been associated with any other cases of Legionnaires' disease, or case who stayed at an accommodation site linked to other cases with date of onset more than two years apart.

Cluster
Two or more cases who stayed at or visited the same commercial accommodation site in the two to ten days before onset of illness and whose onset is within the same two-year period.
A cluster can be additionally categorised as a: * Rapidly evolving cluster: when three or more cases have onset of disease within a three-month period occurring in the six months preceding or following a cluster notification or update. This categorisation indicates a possible recent increase of exposure risk. * Complex cluster: if a cluster involves cases that are associated with staying at one or more accommodation sites also being part of clusters, it is handled as a 'complex cluster'.
If any further cases associated with the cluster site occur more than two years after the last case, they will be reported as new single cases, although the country of infection will receive information on all previous cases linked to the accommodation site regardless of the time period elapsed.

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As at April 2018, 28 EU Member States, two EEA countries and two countries outside the EU/EEA area were contributing or receiving data on TALD cases. ELDSNet has contacts in 30 countries outside the EU/EEA area who are receiving data directly from ELDSNet.

TALD notifications and investigations
All notifications regarding single TALD cases and clusters aim to be sent out within one business day from the reception of the case report. Clusters are reported to the country where the accommodation site is located, the reporting country and all ELDSNet network members. The hosting country is expected to arrange for the accommodation site to be inspected by a competent institution authorised by the national authority such as a local or regional public health authority. This must be accomplished promptly as well as a risk assessment according to guidelines of the country or the European Technical guidelines (2017).

All reported cases
The number of reported cases in the EU/EEA countries has fluctuated during the last ten years (Figure 1)   The majority of cases are reported from countries in the Western part of Europe (Figure 2). Four countries, France, Germany, Italy and Spain usually report the vast majority of cases in the EU/EEA area. In 2015, these four countries they accounted for 69% of all cases. On the other hand, the 15 lowest reporting countries merely reported 3% of all cases.
This shows how unevenly distributed the reported cases are among the EU/EEA countries.
There is a seasonal variation for Legionnaires' disease, and August is the month when most cases are reported to have onset of disease.
Notification rates also increase with age. People older than 50 years of age accounted for 81% of cases with known age and sex in 2015.
Legionnaires' disease is more common in males, with an overall male-to- There is a seasonal variation for LD, and August is the month when most cases are reported to have onset of disease. Notification rates also increase with age.
People older than 50 years of age accounted for 81% of cases with known age and sex in 2015. LD is more common in males, with an overall male-to-female Source: https://ecdc.europa.eu/sites/portal/files/documents/Legionnares-disease-europe-2015.pdf female ratio of 2.5 -3.0 to 1. About 75% of the cases are reported as community-acquired and roughly 20% are travel associated. Healthcareassociated cases represents a considerable proportion of cases in older age groups, but in the total figures this setting represents less than 10%.
The reported mortality rate of Legionnaires' disease in 2015 was 0.8 per million inhabitants, which is consistent with the rates recorded since 2008 which ranged from 0.7 to 0.9 per million inhabitants. Of 4893 cases with a known outcome, 396 were reported to have died giving a case-fatality ratio (CFR) of 8%. Case fatality is higher for older age groups, both in males and females. In individuals above 50 years of age, case fatality is higher. A similar pattern is demonstrated for both males and females.
Almost 90% of cases are reported to have been diagnosed with a urinary antigen test, but there is a large variety in diagnostic tests used in the different EU countries. PCR tests are increasingly used, and in some countries more than 20% of cases are diagnosed with PCR.

Travel-associated cases
The number of reported TALD cases with onset of disease in 2015 was the highest number ever reported to the network with 1141 reported cases There is also a similarity to the overall Legionnaires' disease sex distribution, as over two-thirds (69%) of the reported TALD cases are male. Cases had a median age of 62 years and 82% of cases were aged 50 years or older. Around 90% of the TALD cases are diagnosed using a urinary antigen test. Since the TALD cases are reported in a very timely manner, the clinical outcome of infection is often known for only about half of the cases, and the case-fatality rate for those cases with a reported outcome is around 4%. The TALD cases reported in 2015 were associated with a cumulative total of 1606 stays in various destinations around the world, and 76% were within the EU/EEA area (Figure 4).
In total, 167 new clusters were detected in 2015, and the majority were comprised of two cases. In 60% of the clusters, the first two reported cases were from different countries. Thus, most of these clusters would likely not have been detected without the ELDSNet network and EU

Travel-associated cases
The number of reported TALD cases with onset of disease in 2015 was the highest number ever reported to the network with 1141 reported cases ( Figure   3).   50% of the EU/EEA population. Many countries have a notification rate below 0.5 cases per 100 000 population which has been unchanged for the past five years and unlikely to reflect the true incidence of Legionnaires' disease. It is likely that the lower rates represent a considerable underestimation of the incidence which could be due to both underdiagnosis and underreporting. The European surveillance of the travel-associated cases as performed by ELDSNet is a very good example of how multi-country joint surveillance schemes can facilitate the implementation of preventive measures, and thereby reduce potential exposure sources for travellers at risk for Legionnaires' disease.
were from different countries. Thus, most of these clusters would likely not have been detected without the ELDSNet network and EU surveillance scheme. The number of TALD clusters at the subnational (NUTS2) is shown in Figure 5.