Drug-related infectious diseases — an overview of the methods and definitions used
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, anthrax, 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, although some studies report data for ‘recent injectors’ (e.g. those injected in the last 12 months) among active drug users in contact with 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 the notified or reported number of cases. National notification data of hepatitis B/C are often unreliable due to under-diagnosis (large proportions of new infections are asymptomatic), under-reporting and misclassification of injecting risk. HIV case reporting data are more likely to be of better quality, although they are subject to similar problems. Moreover, HIV case reporting has not yet been fully implemented in some of the countries most affected by AIDS. Other infections may in the future be added to the EMCDDA monitoring system (e.g. other sexually transmitted infections and tuberculosis among drug users), while the EMCDDA collaborates in the European Early Warning and Response System (EWRS — coordinated by the ECDC) regarding outbreaks of serious infections related to (injecting) drug use, such as anthrax, tetanus and wound botulism.
To improve HIV and hepatitis B/C monitoring in IDUs, the EMCDDA follows two lines of work:
- Collecting existing prevalence data (HIV and hepatitis B/C) and notification data (currently, hepatitis B/C notifications; HIV case reports are obtained from ECDC–WHO/Europe) in aggregate format, using a standard data reporting form (‘Standard Table 9’, since 2008 accessible through an online data collection system ‘FONTE’ ).
- 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.
For more information on these tools and methods, see the DRID key indicator page.
The EMCDDA has developed draft guidelines for the national focal points to collect the existing prevalence and notification data and 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 25 years of age) and new IDUs (who have injected for less than two years). These indicators, and especially the HCV data for new IDUs, may be more sensitive to changes in incidence than in prevalence in all IDUs.
In practice, the target group differs slightly between settings: sero-prevalence data from needle exchanges by definition refer to active injectors, while data from hepatitis notifications or public health laboratories may be partly based on former 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 template was included in ‘Standard table 9’ 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. The data provide a general overview 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 broad overview of the situation, including regional variation in levels and trends. Although in general they show a relatively stable prevalence of HIV and hepatitis among IDUs, they have 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.
Finally, in response to the EU Drugs Action Plan 2005–08, 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 several scientific publications are being prepared for publication. The study group is currently working with funding provided by WHO/Europe and the government of the Netherlands.
References
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