Introduction

European HIV/AIDS surveillance started in 1984 with the European Centre for the Epidemiological Surveillance of AIDS (EuroHIV) and the reporting of AIDS cases by 17 countries1. It aims at understanding, improving and sharing HIV-AIDS surveillance data to optimise the prevention, control and management of the disease. This network gradually extended to the 51 member countries of the World Health Organization European Region. After reporting AIDS cases, most European countries have implemented the notification of HIV seropositivity at different dates (1). However, the three countries most affected in the West (France, Italy, and Spain) still have no notification system to report HIV infection at the national level2. This article presents surveillance data on AIDS cases and new diagnoses of HIV infection reported by 30 June 2002 (2).

Methods
Standardised and anonymous data on AIDS cases and new HIV diagnoses as well as the prevalence of HIV infection in target populations (such as injecting drug users (IDU)) are collected every six months through the national coordinators of HIV/AIDS surveillance in the 51 European countries (3). These data are then analysed and published in the six monthly report "Surveillance of HIV/AIDS in Europe" (www.eurohiv.org). To take into account the diversity of the epidemiological situation in the WHO European region, the 51 countries have been classified into three geographical areas: the West (the 15 countries of the European Union, plus Andorra, Iceland, Israel, Malta, Monaco, Norway, San Marino, and Switzerland), the East (the 15 countries of the former Soviet Union), and the Centre (the other countries of the former communist block, plus Turkey) (table).

Results
HIV/AIDS infection in western Europe (figures 1 to 4)
The use of powerful antiretroviral drugs on a large scale since 1996 was followed by a significant decrease in AIDS incidence and deaths among AIDS cases. Starting in 1996, this trend became stronger in 1997, then slowed down the following years. In 2001, AIDS incidence was 22.8 per million population (table). Decreases in AIDS cases have been less marked among persons infected during a heterosexual intercourse ('heterosexuals') than for other transmission groups, so that for the first time in 2001, 'heterosexuals' constituted the largest transmission group (36 %). Most of this group were men (59 % in 2001), and a growing proportion of cases originated from a country where the HIV epidemic generalised (from 24% in 1997 to 34% in 20013, mainly sub-Saharan Africa.

The overall rate of new HIV diagnoses was 54.9 cases per million population in 2001. In western countries for which such data have been available for at least five years, the global rate of new HIV diagnoses appears relatively stable. These data should nonetheless be interpreted cautiously because they highly depend on testing and reporting procedures in each country. The number of new HIV diagnoses reported per year decreased slowly in homo/bisexual men (HBM) and injecting drug users (IDU), but it has constantly increased since 1996 in persons heterosexually infected (+64% between 1997 and 2001).

This increase is due to an increase in cases originating from countries where the HIV epidemic is generalised. It has been observed in several countries (for example Belgium, Ireland, Norway, United Kingdom), but is more marked in the United Kingdom (+144% between 1997 and 2001), where migrants account for 79% of reported cases heterosexually infected in 2001. Data for the first six months of 2002 seem to confirm these trends.
HIV/AIDS infection in central Europe (figures 1,3)

In the Centre, AIDS incidence (<6 cases per million population per year) and the rate of new HIV diagnoses (7-10 cases per million) remain low (table). Numbers of new HIV diagnoses in IDU are low, and almost exclusively diagnosed in Poland (95%). Central Europe reported the majority of paediatric AIDS cases (61%), resulting from an outbreak which occurred in young children in Romania in the 1990s, due to blood transfusions or multiple injections using poorly sterilised equipment.

HIV/AIDS infection in eastern Europe (figures 1,3,5,6)
In the East, the number of newly diagnosed HIV infections has dramatically increased from 233 cases in 1994 to nearly 100 000 reported cases in 2001, representing 348.8 cases per million. In 2001, rates over 100 cases per million population were observed in four countries (Estonia, Latvia, the Russian Federation and Ukraine), and between 15 and 75 cases per million in eight other countries of the region. The epidemic began in 1995 in Ukraine, then spread to the Russian Federation, Belarus and the Republic of Moldova in 1996, Latvia in 1998, Estonia in 2000 and Lithuania in 2002 (data not shown). All countries in this area are affected, including Armenia, Azerbaijan, Georgia and Kazakstan, Kyrgyztan, Uzbekistan.

In 2001, the majority of these infections were diagnosed in IDU (89% excluding cases with no reported risk), males (78%) and young people (82% under 30). The number of cases attributed to heterosexual transmission has also increased (+53% in 2001 compared to 2000). Inversely, the number of cases among HBM is very low and stable (around 100 per year). For a large and increasing number of cases, the mode of transmission is not reported (38% in 2001).

AIDS incidence remains low (<3 cases per million inhabitants), except in Latvia (16.9 cases per million in 2001) and in Ukraine (17.2 cases per million in 2001) (table). Three quarters of AIDS cases in the East are reported with pulmonary tuberculosis as AIDS indicative disease.

Discussion
Western Europe: an endemic and concentrated situation
In western Europe, the large scale use of powerful antiretroviral drugs has widely contributed to the decrease in new AIDS cases and deaths among AIDS cases, especially over the two years following their availability. Despite the increase of new HIV diagnoses in those infected through heterosexual contact, in particular in individuals originating from countries where the infection is generalised, IDU and HBM remain the most affected groups in the West. The prevalence of HIV infection in IDU was 16% in France (national survey based on self reporting of HIV serostatus), and 31% in Spain (national survey based on diagnostic testing) in 1999 (more recent data unavailable) (4). In HBM, HIV prevalence was between 11 and 20% in 2000 in three large cities: Barcelona and London (unlinked anonymous surveys) and Paris (survey based on self reporting of HIV serostatus) (2). Moreover, the recent increase of sexually transmitted infections in HBM in several countries of western Europe (5) suggests a relapse of risky behaviours in this group.
The major challenges currently facing western Europe are to prevent the slackening of safer sex practices and to improve access to HIV testing and health care for all persons infected, especially migrants coming from countries where the infection is generalised.

Central Europe: low level epidemic
Central Europe appears to have been relatively spared by the epidemic. Data on AIDS incidence and new HIV diagnoses, together with data available on prevalence in pregnant women (< 2 per 10 000) or in IDU (< 2% except for Poland where prevalence was 11% in 2000) confirm that this region has generally escaped a large scale dissemination of HIV (4,6-7). However, risk behaviours exist in all countries and it is therefore crucial to maintain effective prevention measures.

Eastern Europe: recent and concentrated epidemics
Since the collapse of the Soviet bloc, the East has been faced with an explosive HIV epidemic concentrated among IDU in an unfavourable socio-economic context (increase in prostitution and drug use and economic crisis). Currently, risk reduction programmes barely cover 10% of the IDU population (7). To contain this epidemic, it is vital to increase the coverage of these programmes. Large-scale heterosexual transmission represents a major risk in this region. The outcome will depend on the nature and extent of contacts between high risk populations (in this case, IDU) and the general population. The number of infections associated with heterosexual transmission remains low but has been increasing significantly for 2-3 years. The low incidence of AIDS in eastern Europe reflects partly the long incubation period of AIDS, but also underreporting in some countries. Inevitably, the East will be faced to a massive AIDS epidemic as a consequence of the current HIV epidemic. This may overwhelm health care services. The HIV epidemic will probably have a negative impact on the control of tuberculosis in this part of the world where the prevalence of tuberculosis and multiresistant strains is already very high, especially as HIV infection and tuberculosis mainly affect the same populations, frequently young and socially disadvantaged.

Comparing epidemiological data on HIV/AIDS at the European level is essential for a better understanding of the dynamics of the epidemic and the impact of prevention programmes. It should also help towards a better assessment of the impact of migrant populations on the HIV/AIDS epidemic in Europe.

Notes
1 Germany, Austria, Belgium, Denmark, Spain, Finland, Greece, Iceland, Italy, Norway, The Netherlands, Poland, United-Kingdom, Sweden, Switzerland, Czeck Republic.
2 Mandatory notifications of HIV diagnoses began in France in January 2003.
3 HIV prevalence among pregnant women consistently > 1%.

Acknowledgements

EuroHIV is a programme funded by the European Commission (contract contrat N°SI2.326442 [2001CVG4-020]) within the framework of the European Surveillance Network for Communicable Diseases, implemented by the European Decision in 1998. We wish to thank the national correspondents of HIV/AIDS surveillance from the 51 countries as well as all the clinicians, biologists and health professionals who make data collection possible.