Seasonal influenza is very common

During ‘average’ seasonal influenza epidemics 5-15% of the population in the Northern hemisphere are affected (WHO, 2009e). When a seasonal outbreak is ‘average’ we speak about an epidemic. When the outbreak is more intense, we speak of a pandemic, i.e. a worldwide and very serious outbreak.

ECDC coordinates the EISN and CNRL

Since September 2008 the coordination of the EISN has been transferred to ECDC . It is assisted in its task by a Coordination Group of experts from the network.

ECDC has surveillance tasks such as to collect, collate, validate, analyse and disseminate relevant data at EU level, operate the dedicated surveillance networks, maintain the database(s) for epidemiological surveillance etc. (For more information see ECDC website).

In addition from September 2008, ECDC is responsible for the coordination of the CNRL. The CNRL has its roots in a collaborative effort to perform influenza surveillance through sentinel networks, which started in 1996 with seven European countries. Over the years, the collaboration was further intensified leading to the creation of the CNRL. The CNRL currently includes the reference laboratories for influenza from all EU Member States and Norway.

The CNRL is closely associated with the WHO through its network of National Influenza Centres (NICs) and collaboration with the WHO-Collaborating Centre for Reference and Research on Influenza.

How the network reports?

The ECDC publishes a weekly surveillance report which is based on data covering a total population of 500 million inhabitants. The weekly surveillance report provides a weekly overview of influenza activity in Europe in the form of a map, a table, graphs and a commentary written by experts from ECDC.

The clinical surveillance of influenza in the EISN is generally based on reports made by sentinel general practitioners. Some of the sentinel surveillance systems also include paediatricians (e.g. the Czech Republic, France and Germany) and physicians with other specialisations (e.g. Slovenia, Lithuania). 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 ILI and few report the number of new cases of ARI. Some networks report both ILI and ARI (ECDC, 2009b).

The sentinel physicians are asked to take nose and/or throat swabs from patients with ILI or ARI. Some sentinel surveillance systems also collect blood samples (e.g. the Czech Republic, Romania and the Slovak Republic). The specimens are sent to the national reference laboratory and are tested for influenza viruses (if positive, subtypes are determined) and other respiratory viruses. 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 physicians to EISN. Specimens (nose swabs, throat swabs and blood samples) can come from a wide range of sources: hospitals, non-sentinel physicians, homes for the elderly, clinics, etc. These data are collected to validate the data provided by the sentinel surveillance systems and to better describe the epidemiology and virology of influenza in each network (ECDC, 2009c).

Trends: no clear trends in peak number of influenza cases since 1996-1997

In Europe there is no clear increase or decrease in the peak incidence of ILI and ARI since 1996-1997. Some developments could have contributed to a decreasing trend, such as a better general health, increased vaccination coverage among risk groups, reduced transmission of the virus due to a decrease in the number of persons per household, and introduction of new antiviral drugs that can reduce the severity of the disease and shorten its duration. On the other hand some developments could have increased the spread of the virus by increasing contacts between people, such as more children visiting day-care facilities, and larger attendance of big events, and a generally increased global mobility as well as an increase of the aging population, which is a known risk group. In addition, the number of people in risk groups increases due to improvements in the (early) diagnosis by GP’s of diseases such as diabetes mellitus and cardiovascular disease. In the coming years the risk population for influenza complications is expected to continue to increase further (Tacken et al., 2008).

Current trends in Novel Influenza A(H1N1) in EU countries

All EU-27 and 4 EFTA countries are reporting cases of pandemic (H1N1) 2009 influenza. On 27 April 2009 the first four confirmed cases of novel influenza A (H1N1) virus were detected in Europe, i.e. in Spain and the United Kingdom. Since then the number of confirmed cases has continued to increase.

For more details see our interactive map with the developments in the number of confirmed novel influenza A(H1N1) cases.

WHO Europe and ECDC are providing constant updated numbers of confirmed cases.