Journal of Medical Virology 80:640–645 (2008) Distribution of Hepatitis C Virus Genotypes Among Injecting Drug Users in Contact With Treatment Centers in Belgium, 2004–2005 M.I. Micalessi, 1 * C. Ge ´ rard, 1 L. Ameye, 2 S. Plasschaert, 2 B. Brochier, 1 and R. Vranckx 3 1 Scientific Institute of Public Health, Virology Section, Department of Microbiology, Juliette Wytsmanstraat 14, Brussels, Belgium 2 Scientific Institute of Public Health, Epidemiology Section, Department of Epidemiology and Toxicology, Juliette Wytsmanstraat 14, Brussels, Belgium 3 Scientific Institute of Public Health, Department of Microbiology, Juliette Wytsmanstraat 14, Brussels, Belgium The aim of this study was to determine the current prevalence of HCV genotypes in injecting drug users recruited at treatment centers all over Belgium, and to analyze if the distribution of genotypes was correlated with demographic characteristics, at-risk behaviors, and co-infection with other viruses. Therefore 147 anti-HCV- positive serum samples were selected for sub- sequent HCV RNA detection and genotyping. HCV RNA could be detected in 98 (67%) of the 147 serum samples. Genotype 1 (38%) and 3 (49%) were the most common genotypes followed by genotype 4 (9%) and genotype 2 (2%). One mixed infection (1%) was detected. The subtype could be determined in 80 cases: genotype 3a was the most prevalent (49%), followed by genotype 1a (16%) and genotype 1b (15%). No significant difference was found between the distribution of genotypes and the location of treatment centers, at-risk behaviors and co-infection with other viruses. Nevertheless, a slight variation over time could be identified (P ¼ 0.06): one in two geno- type 3 drug users started with their injecting drug use in the last 10 years (33% in the period 1995– 1999 and 21% in the period 2000) compared to only one in four genotype 1 drug users (20% in the period 1995–1999 and 9% in the period 2000). J. Med. Virol. 80:640–645, 2008. ß 2008 Wiley-Liss, Inc. KEY WORDS: HCV; genotyping; intravenous drug users; Belgium; LiPA INTRODUCTION Worldwide approximately 170 million people are infected chronically by the hepatitis C virus (HCV) [Lauer and Walker, 2001; Limburg, 2004]. HCV, identified in 1989, is a major cause of chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. The transmission of HCV occurs predominantly parenter- ally. Since 1991, blood and blood products are screened systematically for hepatitis C, so that this route of transmission has strongly decreased. However, an important risk group remains the injecting drug users, through sharing of syringes and paraphernalia like cookers and cotton [Limburg, 2004]. At present, the anti-HCV prevalence rate in injecting drug users in Western Europe ranges from 37% to 98%. Other possible transmission routes are healthcare-related procedures, needle-stick accidents in healthcare, tattooing and body piercing, vertical transmission from mother to neonate, and in a less efficient way sexual transmission [Wasley and Alter, 2000; Leung, 2002; Limburg, 2004]. HCV, a positive-single stranded RNA virus belonging to the family of Flaviviridae, is characterized by high genetic variability. Therefore HCV has been classified into six major genotypes (1 – 6) and into several subtypes (a, b, c, ...) [Simmonds et al., 1993]. The genotypes have a geographically distinct distribution [Lauer and Walker, 2001]. In Western Europe and the United States genotypes 1a and 1b are the most prevalent, followed by genotypes 2 and 3. Genotypes 4, 5, and 6 are predominant in Egypt, South Africa and Southeast Asia, respectively. The genotypes are also associated with specific transmission routes [Cilla et al., 1996; Westin et al., 1999; Limburg, 2004]. For example genotype 3a is common in Europe in the younger population, particularly among injecting drug users, while genotype 1b is strongly associated with transfusion-related HCV. Grant sponsor: Federal Government of Belgium. *Correspondence to: M.I. Micalessi, Scientific Institute of Public Health, Virology Section, Department of Microbiology, Juliette Wytsmanstraat 14, B-1050 Brussels, Belgium. E-mail: isabel.micalessi@iph.fgov.be Accepted 10 January 2008 DOI 10.1002/jmv.21145 Published online in Wiley InterScience (www.interscience.wiley.com) ß 2008 WILEY-LISS, INC.