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Methods and definitions

Drug-related infectious diseases

Drug-related infectious diseases such as HIV and hepatitis B and C are among the most serious health consequences of drug use. Even in countries where HIV prevalence in injecting drug users (IDUs) is low, other infectious diseases, such as hepatitis B/C, sexually transmitted diseases, TB, tetanus, botulism, hepatitis A, HTLV and other infections may disproportionately affect drug users.

IDUs are the target group for measuring prevalence of drug-related infections. They are defined as any person who has ever in their lifetime injected a drug for non-medical purposes. In practice, almost all data on IDUs collected by the EMCDDA relate to ‘ever injectors’ among active drug users who are in contact with drug services.

The EMCDDA is systematically monitoring HIV and hepatitis B and C among injecting drug users (prevalence of antibodies, or other specific markers in the case of hepatitis B). This is as a complement to existing notification and case-reporting systems that follow trends in a number of cases. National notification data are often unreliable due to under-diagnosis, under-reporting, misclassification of injecting risk and the fact that large proportions are asymptomatic cases (hepatitis B/C). In addition, HIV case reporting has not been fully implemented in some of the countries most affected by AIDS, while trends in HIV case reports depend on testing coverage and are not necessarily consistent with trends in measured sero-prevalence. Other infections may in the future be added to the EMCDDA monitoring system (e.g. other sexually transmitted infections, tuberculosis) while a rapid alert system is being maintained to report outbreaks of serious infections, such as tetanus and wound botulism.

To improve HIV and hepatitis B/C monitoring in IDUs, the EMCDDA follows two lines of work:

1. Collecting existing prevalence data (HIV and hepatitis B/C) and notification data (currently hepatitis B/C notifications; HIV case reports were obtained from former EuroHIV, both will in future be obtained from ECDC) in aggregate format using a standard data reporting form (‘standard table 9’, from 2008 accessible through an online data collection system ‘FONTE’).
2. Stimulating new sero-behavioural studies in injecting drug users and stimulating increased screening of IDUs and data collection in routine settings such as drug treatment, by maintaining an expert network to discuss methods and work towards common protocols.

The EMCDDA has developed draft guidelines for the national focal points to collect the existing prevalence and notification data and recently a draft protocol for primary data collection through sero-prevalence studies.

To further improve the comparability of prevalence data in IDUs, data are collected and reported on prevalence of HIV and hepatitis in young IDUs (under age 25) and new IDUs (who have injected less than two years). These indicators, and especially the data for new IDUs, are more sensitive to changes in incidence than is prevalence in all IDUs.

In practice, the target group differs slightly between settings: sero-prevalence data from needle exchanges by definition refer to current injectors (defined as having injected in the last 12 months) while data from hepatitis notifications or public health laboratories may be partly based on ex-injectors, so additional methodological data such as service setting are also collected.

Following discussions during the annual meetings of the EU expert network, a new sheet was included in the standard table in order to collect information on key behavioural characteristics of the IDUs in the studies’ samples. Main items include HIV testing and risk behaviour (e.g. needles or paraphernalia sharing) and other variables related to the risk of contracting a blood-borne infectious disease, e.g. homelessness or sex work.

The aggregate prevalence data collection through the standard reporting form has been successful. In a few years’ time, a general overview could be given of HIV and hepatitis B/C prevalence among IDUs in all EU Member States, going back to 1996 and in part even before. Many countries are able to provide up to date data with national coverage and in many cases there is regional breakdown or data from key regions or cities, often unpublished and recent. These data have proven useful to provide a general overview of the situation, showing regional variation in levels and trends. Although in general they show a relatively stable prevalence of HIV and hepatitis among IDUs, they served to signal some increases in HIV or hepatitis among subgroups of IDUs in some countries.

However, the data are subject to important limitations: the use of varying source-types/settings (drug treatment, low-threshold, prisons, etc.) that may result in different biases, in some cases non-adherence to the basic case definition of ‘ever-IDUs’ that by inclusion of non-IDUs may lead to potentially serious downward bias, and other problems. Improving data quality and comparability proves difficult, as this depends on influencing often well-established data producing systems. Also, to get quality information on trends over time from routine diagnostic data (as opposed to well-defined prevalence studies), it is necessary to understand selection procedures for being tested, and if possible to work towards more standardisation in the criteria for screening of IDUs in contact with services.

In response to the EU Action plan on drugs, the EMCDDA has set up the ‘European study group for mathematical modelling and epidemiological analysis of drug-related infectious diseases’. The group aims to use modelling techniques and data from available epidemiological studies to understand the factors (including interventions) contributing to the large differences observed in the spread of HIV and hepatitis among IDUs in Europe. A first project report with preliminary analyses was finalised in 2007 and six scientific publications are being prepared for publication. For more information, see more...

References

Kretzschmar, M., Wiessing, L., ‘New challenges for mathematical and statistical modeling of HIV and hepatitis C virus in injecting drug users’, AIDS 2008, 22: pp. 1–10.

Sutton, A.J., Hope, V.D., Ncube, F., Matheï, C., Mravcik, V., Sebakova, H., Vallejo, F., Suligoi, B., Wiessing, L., Kretzschmar, M., ‘A comparison between the force of infection estimates for blood-borne viruses in injecting drug user populations across the European Union — A modelling study’, Journal of Viral Hepatitis (in press).

Kretzschmar, M., Wiessing, L. (eds.), ‘Coordination of a working group to develop mathematical and statistical models and analyses of protective factors for HIV infection among injecting drug users’, European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), Lisbon, 2007.

Backmund, M., Reimers, K., Reimer, J., Krausz, M., Zachoval, R., Gölz, J., Klempova, D., Wiessing, L., ‘Protective factors for HIV infection in IDUs — EMCDDA literature review’, European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), Lisbon, 2007.

Vicente, J., Wiessing, L., ‘European Monitoring Centre for Drugs and Drug Addiction annual report 2007: positive assessment of HIV in IDUs though hepatitis C still very high’, Eurosurveillance 2007: 12(11); E071122.6. Available from: http://www.eurosurveillance.org/ew/2007/071122.asp#6

Wiessing, L., Nardone, A., ‘Ongoing HIV and viral hepatitis infections in IDUs across the EU, 2001–2005’, Eurosurveillance 2006: 11(11); 23 November, 2006. http://www.eurosurveillance.org/ew/2006/061123.asp#2

Kontogeorgiou, K., Terzidou, M., Klempova, D., Wiessing, L. (eds.), ‘Protocol for the implementation of the EMCDDA key indicator drug related infectious diseases (DRID)’, draft version 6 October 2006, Project CT.04.P1.337, European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), Lisbon, 2006. https://www.emcdda.europa.eu/?nnodeid=1375.

Reimer, J., Schulte, B., Castells, X., Schafer, I., Polywka, S., Hedrich, D., Wiessing, L., Haasen, C., Backmund, M., Krausz, M., ‘Guidelines for the treatment of hepatitis C virus infection in injection drug users: status quo in the European union countries’, Clinical Infectious Diseases, 2005: 40 Supplement 5: S373–8.

Wiessing, L., Ncube, F., Hedrich, D., Griffiths, P., Hope, V., Gill, N., Hamers, F., de la Fuente, L., Klavs, I., Leinikki, P., Blystad, B., Meheus, A., Rezza, G., Stimson, G., Goldberg, D., for the EMCDDA expert network on drug-related infectious diseases. ‘Surveillance of infectious diseases in IDUs across the EU: information from the EU expert network’, Eurosurveillance Weekly 2004; 8: 040122. http://www.eurosurveillance.org/ew/2004/040122.asp#2

Hope, V., Ncube, F., de Souza, L., Gill, N., Ramsay, M., Goldberg, D., Thomas, D., Smyth, B., Wiessing, L., ‘Shooting up: infections in injecting drug users in the United Kingdom, 2002’, Eurosurveillance Weekly 2004; 8: 040122. http://www.eurosurveillance.org/ew/2004/040122.asp#3