The EUVAC-NET network undertook a questionnaire study on measles surveillance systems in EU member countries, Switzerland, Norway and Iceland. All questionnaires were completed. Surveillance systems for measles are implemented in 16 of the 18 countries. Most countries have some case based data and in all countries the shift is towards case based surveillance for measles, though there are differences between countries concerning case definitions and classifications. A two-dose MMR vaccination schedule is implemented in all the EUVAC-NET countries but methods used for estimation of vaccination coverage are diverse.

Introduction
The aims of a routine vaccination programme are to control, eliminate, or eradicate a disease. Elimination of measles has been shown to be technically feasible with the vaccines currently in use (1), and the World Health Organization (WHO) has prepared a strategic framework for the European Region to eliminate endemic measles by 2007 (2). Surveillance of measles, the immunisation and control programmes, and the collaboration between countries in close contact with each other need to be strengthened to achieve this target. One aim for the EUVAC-NET is therefore to establish a uniform case definition and disease classification, and to define basic epidemiological, clinical, and laboratory data terms for a measles database (3). Available information about existing disease surveillance, vaccination policy, and vaccination coverage is a useful starting point. A questionnaire survey was carried out to assess the data resources available at national level for a minimal data set for measles surveillance in the countries participating in the EUVAC-NET.

Methods An 18 item questionnaire was developed in collaboration between Istituto Superiore di Sanità (ISS) in Rome, Italy, and Statens Serum Institut (SSI) in Copenhagen, Denmark, and sent to gatekeepers representing the participating countries in the EUVAC-NET (the 15 EU countries, Switzerland, Norway, and Iceland). Table 1 gives an overview of information requested about variables used for surveillance.


Table 1. Information requested concerning variables used for surveillance in the EUVAC-NET countries

Results

All questionnaires were completed and returned during the last trimester of 2000. Changes in surveillance systems since then are not taken into account here. Because of the lack of data in the returned questionnaires, information about laboratory methods used to confirm

a case of measles is not included in the results.

At the time of the survey notification of measles was not mandatory in Austria, Belgium, France, and Germany. Austria and Belgium are included in the results only when indicated, whereas information about France, Germany, and Iceland is based on the sentinel surveillance

systems in operation at the time of the survey. In Iceland and Germany, case based mandatory systems were initiated in January 2001, but details about the system attributes are not available and therefore not included here.

Type of data

Surveillance systems for measles are implemented in 16 countries. Thirteen of the countries can be classified as having a case based surveillance system that in principle includes all measles cases, hereafter referred to as a comprehensive surveillance system, and excludes sentinel surveillance. In France and Germany, the sentinel systems provide case based data, whereas the outputs recorded in the national measles surveillance systems are aggregate. In Iceland, all data are aggregate. All countries except Iceland had at least one system with case based data at the time of the survey. Ireland recorded aggregate data before 1st July 2000, when the system changed to case based reporting. Three systems are currently operating in Greece: the traditional mandatory notification system of clinically diagnosed cases (system A) has been in operation since 1951, but the notification rate is low. Systems B and C were both established in 1998 – a sentinel system of internists and paediatricians who practise privately and notify clinically diagnosed cases, and a network of hospital laboratories. In Switzerland physicians and laboratories have notified measles cases since 1999 and sentinel surveillance has been ongoing since 1987; all systems report case based data.

Case definition

In nine countries a measles case is defined solely on clinical grounds while laboratory confirmation is required in seven countries: Denmark, Finland, Netherlands, Norway, Spain, Sweden, and the United Kingdom. With the exception of Finland, the same countries also include cases with an epidemiological link to a laboratory confirmed case.

Four countries apply the specific part of the recommended WHO clinical case definition of measles, "Any person with fever, and maculo-papular rash, and cough, coryza or conjunctivitis," and eight countries apply the non-specific part, "Any person in whom a clinician suspects measles infection." In three countries both components apply to the case definition used (figure). Finland is using only laboratory criteria for diagnosis.

Case classification and linkage with laboratory results

Eight countries, seven of them classified above as having a comprehensive surveillance system for measles, are using the WHO case classification – clinically confirmed or laboratory confirmed. The latter also includes cases with an epidemiological link to a laboratory confirmed case. On the basis of the same definitions, respectively, Portugal is classifying a case as confirmed, probable, or suspected. Table 2 gives an overview of the case classifications used and the linkage between national surveillance systems and laboratory results in the EUVAC-NET countries.

Table 2. Case classifications used in the EUVAC-NET countries and linkage between the national surveillance systems for measles and laboratory results

With the exception of France and Ireland, laboratory data are linked to the national surveillance system in all countries, and in 12 countries the results are reported directly from the laboratory. In Greece a network of hospital based serological laboratories report results as aggregate data (system C).

Information routinely recorded

All 13 countries with a comprehensive surveillance system register the patient’s age, sex, area of residence, and date of notification (table 3). With the exception of Luxembourg, all countries also record the date of disease onset; information on vaccination status is recorded in 11 of the countries, five of them with the number of doses and date of last dose received. Italy registers presence or absence of vaccination, but also the date of last dose received.

Table 3. Information related to the individual case and routinely recorded in the EUVAC-NET countries classified as having a comprehensive surveillance system, n = 13*

*système de surveillance complet : un système spécifique de surveillance des cas, qui, en principe, inclut tous les cas de rougeole / * comprehensive surveillance system: a case specific surveillance system that in principle includes all measles cases
** ID = identifiant / identifier

Ten countries with a comprehensive surveillance system register if a case is imported, and eight of the countries register information on nationality, although in the UK this is done only when the case is imported. Information on epidemiological links is routinely recorded in ten of the countries; eight countries record data about the setting of the outbreak; and six countries record all three variables related to the source of infection. Ten of the countries with a comprehensive surveillance system also record information on disease outcome in terms of admission to hospital, and nine register complications to measles in terms of death (seven countries), encephalitis (two countries), subacute sclerosing panencephalitis (SSPE) (one country). Three countries have open fields for any information related to complications, and two countries record information on permanent sequelae, but without further details.

Vaccination schedule and methods used for estimation of coverage

All countries in the EUVAC-NET have implemented a schedule of two doses of measles, mumps, and rubella (MMR) vaccine. Fifteen countries have a strategy of giving the first dose at age 12-15 months, whereas Finland, Iceland, and Sweden recommend the first measles vaccine to be given at 14-18 months. Twelve countries recommend the second dose to be given at 3-7 years. In Iceland and the Netherlands, the second dose is recommended at 9 years, and in Belgium, Denmark, Norway, and Sweden at 11-12 years. In Ireland, the recommended age for the second dose has recently been reduced to 5-6 years, and a booster is given at 11-12 years if only one previous dose was given, which is also the practice in Italy. Belgium is considering changing administration of the second dose to 6 years of age.

Thirteen of the 18 EUVAC-NET countries have routine surveillance of vaccination coverage in all regions (table 4). In France, coverage is estimated from yearly analysis of 24 month health certificates issued by general practitioners after a mandatory clinical examination of children at 24 months of age. These certificates mention the vaccination status. In Germany, surveys are conducted at school entry, whereas coverage in Italy is estimated by yearly recapitulation sent by the regions. In France, surveys including almost 20 000 children aged 6 years are organised every other year at schools and analysed at local and national level. In Finland, surveys are carried out by sampling 1 000 randomly selected children every other year, who are being followed up for the first two years of life. The estimated vaccination coverage for the whole birth cohort is based on this sampling. In Belgium, cluster surveys (WHO method) are performed separately with variable time intervals in the three communities of Belgium (Brussels, French, and Flemish), and in Luxembourg, surveys are conducted every five years in the whole country. In Norway data are collected ongoing through the Norwegian electronic notification system for vaccination. In Spain, coverage is reported by each of the 17 regions but the Lot quality technique is also in use for monitoring immunisation services.

Table 4. Surveillance of vaccination coverage in the EUVAC-NET countries, n =18

Fourteen countries have data on the number of children vaccinated in any given year, 11 of the countries having routine surveillance in all regions. Germany and Switzerland only record data on the number of vaccine doses distributed, whereas Spain collates data on vaccine doses administered. When estimating the coverage of the first dose of MMR, 15 countries use a numerator containing the number of individuals by birth cohort who received one dose of measles vaccine, whereas Italy and Spain use the number of individuals by year of vaccination. Three countries apply both methods. When estimating the coverage of the second dose, 10 countries use a numerator containing the number of individuals by birth cohort who received two or more measles vaccine doses. Italy uses the year of vaccination, and two countries use both.

In 15 countries the denominator indicates single birth cohorts. In Denmark, the denominator for the first dose of MMR is the birth cohort due for vaccination (the number of individuals at 15 months of age in a given year). In France the denominator is the total number of 24 month health certificates received.

Discussion

Most countries in the EUVAC-NET have some case based data, and in all countries the shift is towards case based surveillance for measles, which is essential to achieve elimination. The quality of data cannot be assessed from this survey, but there are differences between countries with respect to case definitions and case classification, which underline the importance of concerted efforts to meet the agreed WHO definitions.

With respect to the WHO strategy (2) some countries in the EUVAC-NET are in the control phase, others are in the outbreak prevention phase, and a few are moving towards the elimination phase, which implies that case based surveillance should be the goal. Some countries have additional systems to complement a comprehensive surveillance system – for example, sentinel or laboratory based systems, or both – and in some countries, the attributes of surveillance may vary between geopolitical units. Such settings may benefit from focusing on strengthening of the case based surveillance system and linking data to laboratory results, and other data should be integrated or used for validation.

In moving towards a case based surveillance system, one constraint may be that it is difficult to define a cut off rate for the number of cases that should determine when a country should move from aggregate to case based data. Available resources in terms of economy, manpower, and technology, together with political commitment, would determine the feasibility of such a change. In this context the EUVAC-NET should play an important part as a forum for exchanging relevant experiences to the benefit of the participating countries.

A two dose MMR vaccination schedule is implemented in all the EUVAC-NET countries. With respect to the strategic framework for the elimination of measles in the European Region (2,4), predicting the potential for future outbreaks, the likely achievement of elimination, and informing the correct vaccination strategy, an estimate is needed of the age specific proportion of the population susceptible to measles. Vaccination coverage based on birth cohorts is a major component and should be used together with serological survey and disease incidence data, when estimating the susceptibility profile of a population. Most of the countries use a numerator containing the number of individuals by birth cohort, but the methods used in the national systems for estimation of vaccination coverage are diverse. There may be many reasons for this – historical, managerial, economic, etc – and in most circumstances there is probably more than one. At the same time this could be considered as a resource in the EUVAC-NET in terms of a bank of knowledge gained from the experience with the different systems in use. The EUVAC-NET should therefore promote the development of feasible methods to produce valid vaccination coverage data on birth cohorts in a population, on the basis of existing knowledge in the participating countries.

Conclusion

Surveillance of vaccine preventable diseases and vaccination programmes, especially regarding measles, present greater problems in several of the western EU member states than in the rest of Europe. This has been documented by the WHO regional office in Copenhagen (5), and it has been shown that EU member states actually "export" measles to other European countries and other parts of the world (6,7,8). The EUVAC-NET could therefore contribute to the measles control and elimination in the European Region.

The survey results are useful for defining the variables of a minimal dataset to be used in a prototype database for measles in the EUVAC-NET. The results also show that the network should be a valuable tool in the process of strengthening existing case based and laboratory surveillance systems, and the development of high quality methods for surveillance of measles. The experience gained at national level should be shared in the EUVAC-NET to promote and help countries moving from aggregate to case based surveillance. Also methods to reach high quality data on vaccination coverage should be developed by mutual sharing of experience and knowledge within the network. By fulfilling these efforts, the EUVAC-NET can contribute substantially to the WHO aim of eliminating endemic measles in the European Region by 2007 (9,10).

R. Strauss, Ministerium für Soziale Sicherheit und Generationen, Austria
• . Ronveaux, Institut Scientifique de la Santé Publique, Belgium
S. Glismann, Statens Serum Institut, Denmark
I. Davidkin, National Public Health Institute, Finland
D. Levy-Bruhl, Institut de Veille Sanitaire, France
G. Rasch, Robert Koch-Institute, Germany
T. Panagiotopoulos, Institute of Child Health, Greece
H. Briem, Directorate of Health, Iceland
D. O'Flanagan, National Disease Surveillance Centre, Republic of Ireland
L. Vellucci, Ministerio di Sanità, Italy
P. Huberty-Krau, Inspection Sanitaire, Luxembourg
H. Blystad, Statens institutt for folkehelse, Norway
G. Freitas, Direcção-Geral da Saúde, Portugal
C. Amela, Instituto de Salud Carlos III, Spain
A. Tegnell, Smittskyddsinstitutet, Sweden
H. Zimmermann, Gesundheitsministerium, Switzerland
H. De Melker, Rijksinstituut voor de Volksgezondheid en Milieu, Netherlands
J. White, Public Health Laboratory Service Communicable Disease Surveillance Centre, England and Wales

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