Undiagnosed HIV and Hepatitis C infection in people who inject drugs: From new evidence to better practice.

Background: The objective of this study was to estimate the proportion of undiagnosed HIV or Hepatitis C virus (HCV) infection and to assess the risk factors associated with an undiagnosed infection.

Methods: A questionnaire was distributed among people who inject drugs (PWID) in harm reduction centres in Catalonia, Spain 2008-2012 (n=2243). Self-report of HIV and HCV was compared to oral fluid tests to calculate the proportion of undiagnosed infection. Associations of undiagnosed HIV and HCV with age, origin, risk and protective factors of infection and services use were calculated using a Poisson regression model with robust variance.

Results: The sensitivity of HIV self-report was 78.5% (75.2%-81.5%) and of HCV was 81.2% (79.1%-83.2%), being lower in younger and foreign-born PWID. Specificity for HCV was 55.9% (51.6%-60.1%). PWID who engaged in infection risk behaviors had lower risk of being undiagnosed. Being foreign-born and younger increased the risk of undiagnosed infection. PWID who had not accessed medical care in the last 6months had 1.46 (1.10-1.93) times more risk of undiagnosed HIV and 1.37 (1.11-1.70) times more risk of undiagnosed HCV.

Conclusion: Outreach programmes are essential to provide PWID, specially foreign-born and younger PIWD, access to HIV and HCV test.