Sentinel surveillance

The clinical surveillance of influenza in the European Influenza Surveillance Network (EISN) is generally based on reports made by sentinel general practitioners. Some of the sentinel surveillance systems also include paediatricians and physicians with other specialisations. The physicians usually represent 1-5% of physicians working in the country or region.

Most sentinel surveillance systems report data on the number of new cases of influenza-like illness (ILI) or acute respiratory infection (ARI). Some networks report both ILI and ARI.

Sentinel Surveillance Systems of countries participating in EISN
Country  Year ILI surveillance started  Year ARI surveillance started 
Austria  1960   
Belgium  2000  1985 
Bulgaria    2000 
Croatia  1975   
Cyprus  2003  2003 
Czech Republic  2004  1968 
Denmark  1995   
Estonia  2005  2005 
Finland  2013  2013 
France    1984 
Germany    1992 
Greece  2015   
Hungary  1999   
Iceland  2009   
Ireland  2000   
Italy  1996   
Latvia  1995  1995 
Lithuania  1997  1997 
Luxembourg  2003  2003 
Malta  2002   
Netherlands  1970   
Norway  1975   
Poland  2004   
Portugal  1989   
Romania  2000  2000 
Slovakia  1960  2000 
Slovenia  1999  1999 
Spain  1994   
Sweden  1999 (Stopped 2014–15)   
United Kingdom (England)  1964  1964 
United Kingdom (Northern Ireland)  2000  2000 
United Kingdom (Scotland)  1971  2000 
United Kingdom (Wales)  1986   

Reporting time schedule

Surveillance data is reported weekly on Flu News Europe, a collaboration between ECDC and the WHO Regional Office for Europe. The report is based on the data collected by sentinel physicians and reported by the nominated national operational contact points for influenza surveillance to The European Surveillance System (TESSy) at ECDC. Influenza activity is monitored throughout the year in Europe but more intensely from early October (week 40) in one year to the end of May (week 20) the following year.

Laboratory surveillance of influenza

Surveillance of influenza virus infection on a Europe-wide level requires close collaboration between virologists, epidemiologists and sentinel GP networks to generate the data necessary to inform a timely public health response.

Physicians in sentinel networks may take nose and/or throat swabs from a subset of patients with influenza-like illness (ILI) or acute respiratory infection (ARI). Some sentinel surveillance systems also collect blood samples. The specimens are then sent to the national reference laboratory and are tested for influenza viruses. For positive samples, influenza subtypes are determined. These results are used to validate the clinical reports of ILI and ARI.

The national reference laboratories also report influenza test results from non-sentinel surveillance to EISN. Specimens (nose swabs, throat swabs and blood samples) for non-sentinel surveillance can come from a wide range of sources: hospitals, non-sentinel physicians, homes for the elderly, clinics, etc.

A subset of the detected viruses is antigenically and genetically characterised. In addition, the relatedness between the circulating and vaccine strains is evaluated.

Analysis of resistance against neuraminidase inhibitors and adamantanes is also performed by measuring 50% inhibitory concentration (IC50) values, and/or by genotyping of viruses for detection of known drug resistance mutations. In Europe antiviral resistance is monitored by ECDC and WHO based on reports sent by influenza reference laboratories to The European Surveillance System (TESSy).

Data from laboratory surveillance are included in the weekly surveillance updates published on Flu News Europe.

Hospital-based surveillance

Some countries conduct surveillance for hospitalised cases presenting with severe acute respiratory infection (SARI). Depending on the country, all or a subset of SARI patients are tested for influenza virus infection.

A subset of countries reports laboratory-confirmed influenza-positive hospitalized cases every week. Depending on the country, these cases are from intensive care units (ICU) and/or other wards.

Case definitions, populations under surveillance, and data formats differ among the countries.

Data from hospital-based surveillance are included in Flu News Europe.

Mortality surveillance

Surveillance of all-cause mortality in at least 15 European countries is carried out by the EuroMOMO network. EuroMOMO also has a project called FluMOMO that estimates mortality that could be ascribed to influenza.