title: A national cross-sectional study among drug-users in France: epidemiology of HCV and highlight on practical and statistical aspects of the design.
abstract: BACKGROUND
  Epidemiology of HCV infection among drug users (DUs) has been widely studied. Prevalence and sociobehavioural data among DUs are therefore available in most countries but no study has taken into account in the sampling weights one important aspect of the way of life of DUs, namely that they can use one or more specialized services during the study period. In 2004-2005, we conducted a national seroepidemiologic survey of DUs, based on a random sampling design using the Generalised Weight Share Method (GWSM) and on blood testing.
  
  
  METHODS
  A cross-sectional multicenter survey was done among DUs having injected or snorted drugs at least once in their life. We conducted a two stage random survey of DUs selected to represent the diversity of drug use. The fact that DUs can use more than one structure during the study period has an impact on their inclusion probabilities. To calculate a correct sampling weight, we used the GWSM. A sociobehavioral questionnaire was administered by interviewers. Selected DUs were asked to self-collect a fingerprick blood sample on blotting paper.
  
  
  RESULTS
  Of all DUs selected, 1462 (75%) accepted to participate. HCV seroprevalence was 59.8% [95% CI: 50.7-68.3]. Of DUs under 30 years, 28% were HCV seropositive. Of HCV-infected DUs, 27% were unaware of their status. In the month prior to interview, 13% of DUs shared a syringe, 38% other injection parapharnelia and 81% shared a crack pipe. In multivariate analysis, factors independently associated with HCV seropositivity were age over 30, HIV seropositivity, having ever injected drugs, opiate substitution treatment (OST), crack use, and precarious housing.
  
  
  CONCLUSIONS
  This is the first time that blood testing combined to GWSM is applied to a DUs population, which improve the estimate of HCV prevalence. HCV seroprevalence is high, indeed by the youngest DUs. And a large proportion of DUs are not aware of their status. Our multivariate analysis identifies risk factors such as crack consumption and unstable housing.
authors.affiliation: Infectious Diseases Departement, National Institute for Public Health Surveillance, Saint-Maurice, France. m.jauffret@invs.sante.fr
authors.forename: Marie
authors.initials: M
authors.lastname: Jauffret-Roustide
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Strat
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Couturier
authors.forename: Damien
authors.initials: D
authors.lastname: Thierry
authors.forename: Marc
authors.initials: M
authors.lastname: Rondy
authors.forename: Martine
authors.initials: M
authors.lastname: Quaglia
authors.forename: Nicolas
authors.initials: N
authors.lastname: Razafandratsima
authors.forename: Julien
authors.initials: J
authors.lastname: Emmanuelli
authors.forename: Gaelle
authors.initials: G
authors.lastname: Guibert
authors.forename: Francis
authors.initials: F
authors.lastname: Barin
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Desenclos
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D055030:Drug Users / Q000706:statistics & numerical data*; D005602:France / Q000453:epidemiology; D015658:HIV Infections / Q000453:epidemiology; D006526:Hepatitis C / Q000453:epidemiology*; D006801:Humans; D008297:Male; D015999:Multivariate Analysis; D012307:Risk Factors; D016036:Seroepidemiologic Studies; D011795:Surveys and Questionnaires