System

System description

Sentinel influenza surveillance in the WHO European Region is based on nationally organized networks of primary care physicians, mostly general practitioners (GPs), covering at least 1–5% of the population in their countries (see table below). Depending on the country, physicians report the weekly number of patients seen with ILI and/or ARI, or both, to the national focal point for influenza surveillance. Primary care surveillance for influenza in the European Region is based mainly on these sentinel systems (i.e. data are collected and reported only from selected facilities), although some countries collect data on ILI or ARI from all health facilities in the country (universal surveillance). A subset of specimens from sentinel ILI and ARI patients is tested for influenza and respiratory syncytial virus (RSV) infection. In addition, some countries, mainly in the eastern part of the Region, conduct sentinel surveillance for hospitalized cases presenting with SARI, according to standard case definitions. 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. Case definitions, populations under surveillance and data formats differ among these countries. Most countries also report on additional semiquantitative indicators of intensity, geographical spread and trend of influenza activity at the national level. The table below shows the types of surveillance carried out by countries in the WHO European Region.

National influenza centres (NICs) are institutions designated by countries’ ministries of health and recognized by WHO to participate in the work of the WHO Global Influenza Surveillance and Response System. NICs receive respiratory specimens from a range of sources in their countries (both sentinel and so-called non-sentinel sources, such as hospital laboratories, schools, nursing homes and similar settings where influenza outbreaks may have occurred). They provide virological data on the characteristics of circulating influenza viruses according to influenza type and subtype (A(H3N2) and A(H1N1)pdm09) or lineage (B/Victoria or B/Yamagata). Large proportions of both influenza types from non-sentinel sources are not subtyped or ascribed a lineage, in contrast to viruses from sentinel specimens. In addition, influenza viruses are assessed each season for their antigenic and genetic characteristics to determine the extent of their similarity to the viruses included in the seasonal influenza vaccine. The prevalence of mutations that affect pathogenicity or are associated with reduced susceptibility to antiviral drugs is also determined. Furthermore, susceptibility to neuraminidase inhibitor antiviral agents is assessed by phenotypic tests.

Data are reported at the national level to ECDC and the WHO Regional Office for Europe through The European Surveillance System (TESSy) on a weekly basis during the influenza surveillance season (week 40 to week 20 of the following year).

 

Intensity of influenza activity is described as:

  • low = no activity or activity at baseline* level;
  • medium = usual level of activity;
  • high = higher level of activity than usual;
  • very high = exceptionally high level of activity.

 

* Baseline influenza activity is the level at which clinical influenza activity remains throughout the summer and most of the winter.

 

Geographical spread is described as:

  • no activity: either no laboratory-confirmed cases or no evidence of increased or unusual respiratory disease activity;
  • sporadic: isolated cases of laboratory-confirmed influenza virus infection;
  • localized: laboratory-confirmed influenza virus infection limited to one administrative unit in the country (or reporting site);
  • regional: laboratory-confirmed influenza virus infection appearing in multiple but less than 50% of the administrative units of the country (or reporting sites);or
  • widespread: laboratory-confirmed influenza virus infection appearing in 50% or more of the administrative units of the country (or reporting sites).

 

Trend is described as:

  • increasing: evidence that the level of respiratory disease activity is higher than in the previous week;
  • stable: evidence that the level of respiratory disease activity is similar to that in the previous week;or
  • decreasing: evidence that the level of respiratory disease activity is lower than in the previous week.

 

Dominant type is assessed based on data from sentinel and non-sentinel sources.

 

Country, territory and area profiles are available in English here and Russian here.

 

Types of surveillance carried out by countries in the WHO European Region (based on reporting to TESSy)

Country

Primary care surveillance

Hospital surveillance

ILI

ARI

SARI

Laboratory-confirmed influenza

Albania

 

x

x

 

Armeniaa

 X

x

x

 

Austria

X

 

 

 

Azerbaijan

X

 

x

 

Belarus

X

x

x

 

Belguim

X

x

 

 

Bosnia and Herzegovina

X

 

 

 

Bulgaria

 

x

 

 

Croatiab

X

 

 

 

Cyprus

X

x

 

 

Czech Republic

X

x

 

 

Denmark

X

 

 

 

Estonia

X

x

 

 

Finlandb

X

x

 

x

France

X

 

 

X

Georgia

 x

 

X

 

Germany

 

X

 

 

Greece

X

 

 

 

Hungary

X

 

 

 

Iceland

X

 

 

 

Ireland

X

 

 

X

Israel

X

 

 

 

Italy

X

 

 

 

Kazakhstan

X

 x

x

 

Kyrgyzstan

X

x

X

 

Latvia

X

x

 

 

Lithuania

X

x

 

 

Luxembourg

X

 x

 

 

Malta

X

 

 

 

Montenegro

X

 

 

 

Netherlands

X

x

 

 

Norway

X

 

 

 

Poland

X

 

 

 

Portugal

X

 

 

 

Republic of Moldova

X

x

x

 

Romania

X

x

 

X

Russian Federation

X

 x

x

 

Serbia

X

 

x

 

Slovakia

X

x

 

x

Slovenia

X

 x

 

 

Spain

X

 

 

x

Swedenc

 

 

 

x

Switzerland

X

 

 

 

Tajikistan

X

 

 

The former Yugoslav Repebulic of Macedonia

 x

 

 

 

Turkey

X

 

 

 

Turkmenistan

 x

 x

 x

 

Ukraine

 x

 x

x

 

United Kingdom

 

 

 

 x 

  England

X

x

 

 

  Northern Ireland

X

x

 

 

  Scotland

X

 

 

        Wales

X

 

 

 

Uzbekistan

X

X

 

 

a ILI data are reported but not included for the 2015–2016 season to ensure consistent quality of data.

b ILI/ARI data are available but no denominator is reported.

c Hospital surveillance only includes patients in intensive care.

 

Virus characteristics

In addition to sentinel sources, specimens from non-sentinel sources – such as hospitals, schools, nursing homes and other care institutions – are collected and tested. For both sentinel and non-sentinel sources, a selection of influenza viruses representative of those circulating is characterized genetically, directly from clinical specimens or from viruses isolated in cells or eggs.