Contents :
Introduction
Influenza is an important public health problem in the industrialised world. It is associated with higher general practice consultation rates [1], increased hospital admissions [2] and excess deaths [3]. It must also be considered in terms of increased days lost due to absence from work and in health care planning. Major worldwide influenza pandemics occurred in 1918-19 ('Spanish flu' H1N1 influenza; +20 million deaths), 1957 ('Asian' H2N2 influenza) and 1968-69 ('Hong Kong' H3N2 influenza).
National networks for the clinical and virological surveillance of influenza have existed in Europe since the 1950s. In the late 1980s efforts were made to improve the clinical reports from sentinel physicians by integrating virological surveillance systems and by collecting data on a European level.
The first European project was the Eurosentinel scheme (1987-1991), this was followed by the ENS-CARE Influenza Early Warning Scheme (1992-1994) [4, 5] and the European Influenza Surveillance Scheme (EISS; 1995-) [6, 7]. EISS has received funding from Home & Consumer Protection Directorate-General of the European Commission since November 1999 and from industry since September 2000.
Objectives
Membership
- to facilitate the rapid exchange of information on influenza activity in Europe;
- to combine clinical and virological data in the same population;
- to identify causal viruses in the population and recognise virological changes;
- to provide standardised information of high quality.
All countries in Europe are welcome to join EISS. Full members must meet the following criteria:
A total of 11 EU (Belgium, Denmark, France, Germany, Ireland, Italy, the Netherlands, Portugal, Spain, Sweden and the United Kingdom) and 3 non-EU states (the Czech Republic, Slovenia and Switzerland) are presently members of EISS. Since Scotland and Wales have their own influenza surveillance networks, there are 16 networks in EISS. With the exception of the Spanish network, all networks are national; the Spanish influenza surveillance network is made up of 6 regional networks covering 53% of the total population in Spain.
- the network is nationally or regionally representative;
- the authority of the network is recognised by the national or regional health authority in the country or region;
- clinical surveillance and virological surveillance are integrated in the same population (community);
- the network has functioned successfully for two years;
- the network can deliver data on a weekly basis.
Two networks are "associate" members of EISS: the Irish and the Swedish networks. The Irish network is an "associate" member because it has not yet been in operation for two years and the Swedish one because it does not yet combine clinical and virological data in the same population.
Methods
The clinical surveillance of influenza by the networks that are members of EISS is generally based on reports made by sentinel general practitioners (see table 1). Some of the sentinel surveillance systems also include paediatricians (the Czech Republic, France, Germany, Italy, Slovenia, Spain, Switzerland) and physicians with other specialisations (Slovenia and Switzerland). The physicians usually represent 1-5% of physicians working in the country, community or region.
The case definitions and denominator populations used for the clinical surveillance of influenza vary by network. Most sentinel surveillance systems report data on the number of new cases of influenza-like illness (Denmark, the Netherlands, England, Ireland, Italy, Portugal, Scotland, Slovenia, Spain, Sweden, Switzerland and Wales), whilst others report the number of new cases of acute respiratory illness (Belgium, the Czech Republic, France and Germany) - see table 1.
Some sentinel surveillance systems have denominator populations which are based on patient lists (the Czech Republic, England, the Netherlands, Ireland, Italy, Portugal, Scotland, Slovenia, Spain, Sweden, Wales) and others which are based on the total number of consultations (Belgium, Denmark, France, Germany and Switzerland). Surveillance systems with population denominators can present the number of cases per 100,000 population and those with consultation denominators the number of cases per 100 consultations (%).
The sentinel physicians are asked to take nose and/or throat swabs from patients with influenza-like illness or acute respiratory infection (depending on the sentinel surveillance system - see above and table 1) and to send these to a central laboratory. The swabs are tested for influenza viruses (if positive, subtypes are determined) and a panel of other respiratory viruses (including respiratory syncytial virus infections) - see table 2.
Table 1: Characteristics of the sentinel surveillance systems participating in EISS
Country Population surveyed (year) Physicians (year) Numerator Denominator Threshold rate EU networks: Belgium - 60 GPs (2000) ARI (case definition) Consultations 2.6% of consultations Denmark - 100 GPs (2000) ILI (case definition) Consultations 4% of consultations England 600,000 inhabitants (1999) 333 GPs (1999) ILI (no case definition) Catchment population 50 cases per 100,000 population France - 368 GPs and 71 paediatricians (2000) ARI Consultations 13.5% of all consultations Germany - 551 GPs and paediatricians (1999) ARI Consultations 10% of all consultations Ireland 57,000 inhabitants (2000) 32 GPs(2000) ILI (case definition) Catchment population - Italy 790,000 inhabitants (2000) 460 GPs and 40 paediatricians (2000) ILI (case definition) Catchment population - The Netherlands 155,000 inhabitants (2000) 67 GPs (2000) ILI (case definition) Catchment population 55 cases per 100,000 population Portugal 305,000 inhabitants 200 GPs (1999) ILI (case definition) Catchment population 51 cases per 100,000 population Scotland 400,000 inhabitants (2000) 90 GPs (2000) ILI (no case definition) Catchment population 1000 cases per 100,000 population Spain 112,000 inhabitants 200 GPs and 60 paediatricians (2000) ILI (case definition) Catchment population 114 cases per 100,000 population Sweden 240,000 inhabitants (2000) 40 GPs (2000) ILI (no case definition) Catchment population - Wales 215,000 inhabitants (2000) 30 GPs (2000) ILI (case definition) Catchment population 400 cases per 100,000 population Other networks: Czech Rep. 50% of the total population 2230 GPs and 1240 peadiatricians (2000) ARI (case definition) Catchment population - Slovenia 82,100 inhabitants (2000) 11 GPs, 14 paediatricians, 19 school and youth health service physicians (2000) ILI (case definition) Catchment population - Switzerland - 154 GPs, 68 internists and 43 paediatricians (2000) ILI (case definition) Consultations 1.5% of consultations
GPs = general practitioners
ILI = influenza-like illness
ARI = acute respiratory illness
Table 2: Characteristics of the virological surveillance systems participating in EISS
Country Virus culture methods Additional tests EU networks: Belgium Madin Darby Canine Kidney IF Denmark Madin Darby Canine Kidney ELISA England Madin Darby Canine Kidney /
Rhesus Monkey KidneyCall-EIA / RT-PCR France Madin Darby Canine Kidney IF / ELISA Germany Madin Darby Canine Kidney RT-PCR / IF / ELISA Ireland Madin Darby Canine Kidney IF / PCR Italy Eggs and Cell Lines IF / RT-PCR The Netherlands tertiary Monkey Kidney None Portugal Madin Darby Canine Kidney /
EGGSELISA / RT-PCR Scotland - - Spain Madin Darby Canine Kidney IF / ELISA Sweden Madin Darby Canine Kidney IF / PCR Wales Rhesus Monkey Kidney Direct IF / PCR Other networks: Czech Republic Eggs and Cell Lines ELISA Slovenia Madin Darby Canine Kidney IF / ELISA Switzerland Madin Darby Canine Kidney IF
During the influenza season (week 40 to week 20 of the following year), the clinical and virological co-ordination centre in each network collects data on influenza activity during the previous week. The data is processed, analysed and assessed before being entered into the EISS database using an Internet application (www.eiss.org) [6]. The Internet application allows EISS members to view influenza activity in the other networks and to launch detailed clinical and virological queries. Maps, figures, tables and data from previous years can also be downloaded from the database. This part of the Internet application is only accessible to authorised persons.
The EISS web site (www.eiss.org) also has a number of public pages which provide information on the surveillance scheme, useful links and the Weekly Electronic Bulletin (EISS WEB). The Bulletin provides a weekly overview of influenza activity in Europe in the form of a map, a table and a commentary written by experts from the EISS group (see: EISS WEB). It is based on data entered into the EISS database by Thursday 9:00 (CET), it appears every Friday at 12:00 (CET) and it concerns data collected during the previous week.
EISS has five levels of influenza activity:
- no activity;
- sporadic activity;
- local activity;
- regional activity;
- widespread activity.
Results
The 2000-2001 influenza season:
See the EISS Weekly Electronic Bulletins (EISS WEB) and the EISS maps for the previous three weeks (EISS maps).
The 1999-2000 influenza season (largely taken from reference [8; click here]):
Eleven countries took an active part in EISS during the 1999-2000 season: Belgium, the Czech Republic, Denmark, France, Germany, Great Britain, Italy, the Netherlands, Portugal, Spain and Switzerland. Sweden joined the scheme at the beginning of 2000.
Influenza A virus was first detected in swabs obtained by sentinel physicians in week 40 of 1999 in France. This virus was reported in week 41 in Belgium, Great Britain and the Czech Republic; in week 43 in Germany and Portugal; in week 45 in Spain and the Netherlands; in week 46 in Denmark and Switzerland; and finally in week 47 in Italy. The subtype A (H3N2) predominated in all participating networks; the strains analysed were antigenically linked to the vaccine variant A/Sydney/5/97 (H3N2) or A/Moscow/10/99 (H3N2).
Influenza A(H1N1) viruses were identified very sporadically in all countries except Spain. Type B viruses were first detected in Belgium in the last week of 1999, then in Great Britain (week 2, 2000), Germany (week 4, 2000) and Italy (week 5, 2000). Influenza B only circulated significantly in Great Britain, towards the end of the activity period of influenza (weeks 2, 4 and 5, 2000). The strains of influenza B which were analysed were antigenically close to the vaccine variant B/Yamanashi/166/99.
The rates of acute respiratory illness or influenza-like illness (ILI) per 100 consultations or ILI per 100,000 population generally peaked at the same time as the rates of detection of influenza viruses in the general practices. Maximum rates were generally recorded between weeks 51 (1999) and 5 (2000), with a peak in weeks 1 and 2 of 2000, although some national variations were seen (see figure: Eurosurveillance article 2000).
The maximum levels reached in the 1999-2000 season were defined as follows:
Widespread activity: Belgium, the Czech Republic, France, Germany,
Italy, the Netherlands, Spain and SwitzerlandRegional activity: Denmark and Great Britain Sporadic activity: Portugal
The 1997/1998 influenza season: See: Eurosurveillance article 1998 [9]
Conclusions
EISS is a modern and efficient European surveillance system which collects high quality data, combining both clinical and virological information. By using an Internet-based platform, it is easily accessible and provides timely information. These two characteristics are very important, as the scheme needs to be in a position to react to the emergence of a new virus strain and a possible influenza pandemic in Europe.
EISS allows national experts to better assess influenza activity in Europe and provide more accurate epidemiological and virological information to their health care systems, governments and the general public. Important future projects include: standardising the main indicators collected, determining epidemic thresholds of influenza activity for each network, and initiating laboratory quality assurance controls on a continental level.
References
- Mc Cormick A, Fleming D, Charlton M. Morbidity statistics from general practice: fourth national study 1991-1992. London: HMSO 1995. (Series MB5 no 3).
- Glezen WP. Serious morbidity and mortality associated with influenza epidemics. Epidemiological Review 1982; 4: 25-44.
- Fleming DM. The contribution of influenza to combined acute respiratory infections, hospital admissions, and deaths in winter. Communicable Disease and Public Health 2000; 3: 32-38.
- Snacken R, Bensadon M, Strauss A. The CARE Telematics Network for the surveillance of influenza in Europe. Methods of Information in Medicine 1995, 34, 518-522.
- Fleming DM and Cohen JM. Experience of European Collaboration in Influenza surveillance in the winter 1993-1994. J. Public Health Medicine 1996; 18: 133-142.
- Snacken R, Manuguerra JC, Taylor P. European Influenza Surveillance Scheme on the Internet. Methods of Information in Medicine 1998; 37, 266-270.
- Aymard M, Valette M, Lina B, Thouvenot D, the members of Groupe Régional d'Observation de la Grippe and European Influenza Surveillance Scheme. Vaccine 1999: 17: S30-S41.
- Manuguerra JC, Mosnier A on behalf of EISS (European Influenza Surveillance Scheme). Surveillance of influenza in Europe from October 1999 to February 2000. Eurosurveillance 2000; 5: 63-68 [Eurosurveillance article 2000].
- Zambon M. Sentinel Surveillance of influenza in Europe, 1997/1998. Eurosurveillance 1998; 3: 29-31 [Eurosurveillance article 1998].
Written on behalf of the EISS Working Group* by John Paget and Koos van der Velden, EISS co-ordination centre, Netherlands Institute for Health Services Research (Nivel), the Netherlands.
* Aymard M (France), Bartelds AIM (the Netherlands), Charlier N (Belgium), Christie P (Scotland), Cohen J-M (France), Falcăo IM (Portugal), Fleming DM (England), Grauballe P (Denmark), Havlícková M (the Czech Republic), Heckler R (Germany), Heijnen M-L (the Netherlands), de Jong JC (the Netherlands), Lina B (France), Linde A (Sweden), Manuguerra J-C (France), Marinho Falcao I (Portugal), de Mateos S (Spain), Mensi C (Italy), Mosnier A (France), Müller D (Switzerland), Mullins N (Ireland), Nolan D (Ireland), O'Flanagan D (Ireland), Perez-Brena P (Spain), Pregliasco F (Italy), Prosenc K (Slovenia), Rebelo de Andrade H (Portugal), Samuelsson S (Denmark), Schweiger B (Germany), Socan M (Slovenia), Thomas D (Wales), Thomas Y (Switzerland), Tumova B (the Czech Republic), Uphoff H (Germany), Valette M (France), Vega TA (Spain), Watson J (England), van der Werf S (France), Yane F (Belgium) and Zambon M (England). See: EISS contacts.
Acknowledgements
EISS is funded by the DG Health & Consumer Protection of the European Commission. EISS also receives funding from GlaxoSmithKline and Roche.
EISS would not exist without the regular participation of the sentinel physicians across Europe. We would like to thank them for making this surveillance system possible.
For technical correspondence only.