INFECTIOUS DISEASES Do HIV disease progression and HAART response vary among injecting drug users in Europe? Liselotte van Asten 1 , Robert Zangerle 2 , Ildefonso Herna´ndez Aguado 3 , Faroudy Boufassa 4 , Barbara Broers 5 , Raymond P. Brettle 6 , J. Roy Robertson 7 , Jim McMenamin 8 , Roel A. Coutinho 1,9 & Maria Prins 1 1 Municipal Health Service, Cluster Infectious Diseases, Amsterdam, The Netherlands; 2 AIDS Unit, University of Innsbruck, Innsbruck, Austria; 3 On behalf of the Valencian HIV Seroconversion Study, Department of Public Health, Miguel Hernandez University, Alicante, Spain; 4 SEROCO study group, Inserm U 292, Ho ˆpital de Bice ˆtre, Le Kremlin Bice ˆtre, France; 5 Division of Infectious Diseases, Geneva University Hospital, Geneva, Switzerland; 6 Infectious Diseases Unit, Western General Hospital, Edinburgh, UK; 7 Edinburgh Drug Addiction Study, Muirhouse Medical Group, Edinburgh, UK; 8 Scottish Center for Infection and Environmental Health, Glasgow, Scotland; 9 Department of Human Retrovirology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands Accepted in revised form 18 July 2005 Abstract. Prior to HAART availability, there was no evidence of a geographical variation in HIV disease progression among injecting drug users (IDU) from different European regions. Nowadays, factors of importance regarding HIV disease progression in the face of HAART availability, such as HAART access, adherence, and the organization of care for IDU may differ across Europe. Therefore we studied HIV dis- ease progression in a European study of IDU with known dates of HIV-seroconversion. Results show that with ongoing HAART availability, the risk of HIV disease progression has continued to decrease. When accounting for pre-AIDS death (in AIDS analyses) and non-natural deaths (suicide, overdose, accidents and homicide, in analyses of death) which are common among IDU, the risk of AIDS and death has decreased by as much as 65% and 75%, respec- tively, in 2000/2001. Results show little geographic variation in progression to AIDS. All-cause mortality was higher in IDU from Glasgow than elsewhere, while in the Valencian region (Spain) IDU were at a significantly lower risk of non-natural deaths. The timing of HAART initiation by treatment-naı¨ve IDU likewise differed across Europe: IDU in Amsterdam, Innsbruck, and Edinburgh started at significantly lower CD4 counts than IDU in Paris, Geneva, Glas- gow, and the Valencian region, but the subsequent short-term immune response was similar. In conclu- sion, the risk in progression to AIDS or natural death is similar across western Europe although IDU across Europe differ in other factors, such as the risk of non- natural death and the timing of HAART initiation. Key words: Europe, Highly Active Antiretroviral Therapy, HIV disease progression, Injecting drug users Introduction Since highly active antiretroviral therapy (HAART) became generally available, the risk of HIV disease progression has greatly decreased among injecting drug users (IDU), although not as much as in other HIV-infected groups [1–7]. In general, IDU are less likely to be on HAART [8, 9], and are less com- pliant than other HIV-infected individuals [10]; in those taking [11–14] HAART, the immunological and virological responses are less pronounced in the short term [15–17] and in the long term [18]. The rate of coinfections is high among IDU and hepa- titis C virus (HCV) infection has also been sug- gested to play a role in the decreased effect of HAART seen in this group [1]. All these factors may differ from country to country, as also the specific antiretroviral drug combinations prescribed and the general approach to patient management and the organisation of care for HIV-infected drug users. Prior to HAART availability, there seemed to be no geographical variation in HIV disease progression among IDU from different European regions [19]. When HAART first became generally available (mid 1996–1997), the probability for IDU to initiate HA- ART likewise seemed not to vary across Europe [8]. However, data on regional differences thereafter are lacking. Therefore we studied whether the rates of HIV disease progression and response to HAART vary among European IDU in different countries since HAART became widespread, using data from a collaborative study of IDU cohorts from 7 different cities or regions in Europe. European Journal of Epidemiology (2005) 20: 795–804 Ó Springer 2005 DOI 10.1007/s10654-005-1049-0