The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), a decentralised technical agency of the European Union (EU), is charged with monitoring the drugs phenomenon in Europe. The public health aspects include the surveillance of infections in drug users, which is mainly based on prevalence survey data such as HCV, hepatitis B virus (HBV) and HIV antibody prevalence among injecting drug users (IDUs) in drug treatment and other settings [8,9]. For HCV, these monitoring activities have been complemented by a centralised collection and reporting of available data on notifications of HCV infection. The aim of this is to add information to the data collected through the surveillance of the prevalence of HCV among IDUs, in order to better inform and influence policies at the European level. The monitoring of HCV notifications was initiated at a time when no other institution or expert network collected these data at the European level. Due to limitations in EMCDDA resources and its mandate, this activity has so far been restricted to collecting the data as reported at the national level. However, the need for a European standardisation of national hepatitis C surveillance systems was already identified in 1998 among the then 15 EU member states [10].

In this paper, we present and discuss the sources of information and data collected so far. This may provide an up-to-date basis to improve the comparability and quality of data reporting and increase their usefulness at the European level.

Methods

The EMCDDA collects data on HCV notifications annually through national focal points in charge of drugs and drug addiction surveillance. The national focal points are either interdepartmental bodies (for example, located in ministries of health, internal affairs or justice) or technical governmental institutions carrying out research and monitoring of the drugs phenomenon at the national level. The national focal points are responsible for the collection and reporting to the EMCDDA of a large number of drugs-related data from different national sources. In the case of HCV notifications, the national focal points use a standard reporting questionnaire (the HCV notifications part of ‘Standard Table 9’, available from: http://www.emcdda.europa.eu/?nnodeid=1375). They request their responsible health authorities (e.g. virologists or epidemiologists at the national institute of infectious disease surveillance) to provide aggregated data, including the total number of cases of HCV infection notified by physicians, and, if possible, to specify if these are acute or chronic cases; they also request the number of cases with known risk factor and the number attributed to IDUs. From this information, it is possible to observe trends in the total number of notified cases of hepatitis C, as well as the proportion of IDUs among the cases with valid information on exposure category. Data are also available broken down by gender, age group and the time since first injection. Information on methodology, describing the national surveillance systems, include the use of a unique identifier, the need for laboratory confirmation, and the case definition for HCV infection, as well as the name of the principal investigator responsible for the surveillance at the national level, his/her institution (e.g. national institute of infectious disease surveillance) and relevant bibliographic references.

Results

The number of countries providing data has increased from two in 1999 (providing data back to 1992) to 17 (most recent years of reporting range from 2003 to 2006), of 30 countries currently working with the EMCDDA (27 EU member states, Norway, Croatia and Turkey). One country (the United Kingdom – England and Wales) reported that data were not statutory notifications but laboratory reports, although this information was not collected in a standard way for other countries (Table 1).

All 17 countries reported requiring laboratory confirmation. In eight countries, HCV-RNA results were reportedly collected. Case definitions were provided by all countries, but varied, and did not always seem to be consistent with the EU case definition [11]. The definitions, as reported to EMCDDA, combined clinical, biological and serological criteria (Table 1). Twelve countries used a unique identifier to prevent double counts.

Seven of the 17 countries provided combined data for acute and chronic cases, four provided separate data, and six provided only data for acute IDU cases.

In 2006, 12 countries reported their total number of notified cases, of which five countries reported a total of 22,050 combined acute or chronic cases, one country (Denmark) reported 300 chronic cases, and seven countries (including Denmark) reported a total of 400 acute cases. Eleven of the 12 countries provided the number of notifications with known risk factors. The proportion of notified cases with known risk factor has increased slightly (from 40% in 2001 to 43% in 2006) but on the whole it has remained very low. In 2006, this proportion varied across countries, from 8% of cases in the UK (England and Wales) to 88% in Denmark (Table 2).

Among eight countries reporting over 50 IDU-related cases in 2006 or the latest year available, the proportion of IDUs among all cases with known risk category ranged between 74% and 100%, with the exception of Germany (35%) and Croatia (54%) (Figure).

Discussion

Many EU member states are able to report HCV notification data and at least 17 countries can provide the number and proportion of IDUs among reported cases, adding to the information collected on prevalence of infection among IDUs [9]. 

Methodologically, the national surveillance systems seem to differ considerably in the definition of HCV infection, thus strongly limiting the comparability between countries, even though these data may still provide information regarding trends over time. For a majority of HCV cases reported, the risk factors are unknown or not available for surveillance purposes thus severely limiting their interpretability.

The EMCDDA recommends that countries provide separate data on acute and chronic cases. Better data on acute cases provide a more accurate picture of the current epidemiology of HCV whereas chronic cases reflect a past epidemiology. However, hepatitis C is often asymptomatic in the acute phase, and therefore not diagnosed. Also, as there are few methods for actually identifying the acute cases and distinguishing them from the chronic ones, it is still not entirely clear if a distinction between these categories is useful. Better methods are needed to identify and diagnose acute cases, and it may also be helpful to concentrate on young age groups (15-19, 20-24 years), where there can be relatively high assurance of recent infection. Moreover, the low proportion (and number) of acute cases that are notified often precludes their use as an indicator of new transmission. A study in Seattle in the United States (US) estimated that less than 5.7% and possibly around 1.5% of IDUs who acquire HCV infection would be notified [12]. On the other hand, a recent report from the US suggests that enhanced surveillance approaches may detect outbreaks of new infections in IDUs [13]. For diagnosed chronic cases in regular contact with the healthcare system, it might be expected that notification rates are very high. However, in Denmark it was recently found that only 50% of these had been notified to the national register [14].

There are thus considerable problems in comparing and interpreting the available notifications data, especially when used as an indicator of true incidence of HCV infection, due to the very large proportion of asymptomatic infections, coupled with under-diagnosis, underreporting and the differences in national notification systems. Following the changes in proportions of specific transmission categories over time (e.g. the percentage IDUs among cases), rather than absolute counts or population rates, may provide more comparable information on trends in hepatitis C infection among different risk groups. Given the limitations of the data, the EMCDDA has so far mainly reported the proportion of IDUs among all cases with known transmission risk [9].
 
The proportion of IDUs among all cases with known risk factor is high in most countries, indicating that IDUs still constitute a major, in most European countries even the largest, risk group for acquiring HCV infection. In the data presented here, some countries report changes over time in the proportion of IDUs.

It cannot be excluded, however, that the high proportion of IDUs among cases observed in many countries is partly the result of specific screening programmes among IDUs, resulting in higher detection rates compared to other risk groups.  Likewise, some countries that report relatively low proportion of IDUs among the cases with known transmission risk, suggesting differences in the epidemiology of HCV, may practice more intensive screening of other populations at risk than IDUs, the low proportion thus resulting from different HCV screening policies. In addition, there may be differences in the way the transmission risk is being assessed or reported.

An important improvement to the monitoring system would be to obtain further information regarding the legal status of the notification system (mandatory or voluntary), and this information is currently being collected by the European Centre for Disease Prevention and Control (ECDC). Equally important would be to gather information regarding the estimated exhaustivity of the system for reporting incident or prevalent cases. Regarding the unavailable data (e.g. countries reporting only IDU-related cases or providing combined acute and chronic cases), it would be important to know whether more information is available at the country level. Surveillance systems are still heterogeneous and difficult to compare and a minimal standardisation is a prerequisite for an improved European surveillance of HCV infection [10]. There is a pressing need to improve the HCV surveillance systems in Europe and, ultimately, to establish a more standardised European approach, which will be the subject of upcoming expert meetings at the ECDC. A good understanding of the epidemiology of HCV in Europe is not likely to be based on one single method, such as collecting notifications data, but on a combination of complementary surveillance systems [15] focused on both the general population and the specific populations at risk such as IDUs.

The public health importance and the implications of the HCV epidemic are major issues for Europe. An appropriate monitoring of the newly acquired HCV infections, the associated risk factors and the prevalence and burden of infection across Europe is needed. This should help to target prevention and screening programmes at those who are most at risk of infection, specifically the IDU population, and to allocate services for treatment.

Acknowledgments
We thank all national focal points and colleagues at national level, as well as the EMCDDA expert group on drug-related infectious diseases for providing the data here described. Else Smith, the Danish National Board of Health, having contributed when working at Statens Serum Institut, and Norbert Frost and Danica Klempova, EMCDDA, have provided important contributions.

Note: The EMCDDA collects similar data on national hepatitis B notifications, as well as HCV and HBV seroprevalence data from sentinel and national serological testing in samples of IDUs and it coordinates a European expert network on drug related infectious diseases (mainly hepatitis B, C and HIV) among injecting drug users. For HCV notifications and other infectious diseases data up to 2005 see: http://www.emcdda.europa.eu/stats07/INF

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