title: Identification of hidden key hepatitis C populations: an evaluation of screening practices using mixed epidemiological methods.
abstract: BACKGROUND
  Hepatitis C virus (HCV) is a major cause of liver diseases worldwide. Due to its asymptomatic nature, screening is necessary for identification. Because screening of the total population is not cost effective, it is important to identify which risk factors for positivity characterize the key populations in which targeting of screening yields the highest numbers of HCV positives, and assess which of these key populations have remained hidden to current care.
  
  
  METHODS
  Laboratory registry data (2002-2008) were retrieved for all HCV tests (23,800) in the south of the Netherlands (adult population 500,000). Screening trends were tested using Poisson regression and chi-square tests. Risk factors for HCV positivity were assessed using a logistic regression. The hidden HCV-positive population was estimated by a capture-recapture approach.
  
  
  RESULTS
  The number of tests increased over time (2,388 to 4,149, p<.01). Nevertheless, the positivity rate among those screened decreased between 2002 and 2008 (6.3% to 2.1%, p<.01). The population prevalence was estimated to be 0.49% (95%CI 0.41-0.59). Of all HCV-positive patients, 66% were hidden to current screening practices. Risk factors associated with positivity were low socio-economic status, male sex, and age between 36-55. In future screening 48% (95%CI 37-63) of total patients and 47% (95%CI 32-70) of hidden patients can be identified by targeting 9% (men with low socio-economic status, between 36-55 years old) of the total population.
  
  
  CONCLUSIONS
  Although the current HCV screening policy increasingly addresses high-risk populations, it only reaches one third of positive patients. This study shows that combining easily identifiable demographic risk factors can be used to identify key populations as a likely target for effective HCV screening. We recommend strengthening screening among middle-aged man, living in low socio-economic neighborhoods.
authors.affiliation: Department of Sexual Health, Infectious Diseases and Environmental Health, South Limburg Public Health Service, GGD Zuid Limburg, Geleen, The Netherlands. angelique.vermeiren@ggdzl.nl
authors.forename: Angelique P A
authors.initials: AP
authors.lastname: Vermeiren
authors.forename: Nicole H T M
authors.initials: NH
authors.lastname: Dukers-Muijrers
authors.forename: Inge H M
authors.initials: IH
authors.lastname: van Loo
authors.forename: Frans
authors.initials: F
authors.lastname: Stals
authors.forename: Dirk W
authors.initials: DW
authors.lastname: van Dam
authors.forename: Ton
authors.initials: T
authors.lastname: Ambergen
authors.forename: Christian J P A
authors.initials: CJ
authors.lastname: Hoebe
mesh_terms: D000328:Adult; D000367:Age Factors; D006526:Hepatitis C / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D016012:Poisson Distribution; D015995:Prevalence; D012044:Regression Analysis; D012307:Risk Factors; D012737:Sex Factors; D012959:Socioeconomic Factors