Hepatitis C virus-specific immune responses in noninjecting drug users.

Noninjection drug use, although recognized as an emerging risk factor for acquisition of other blood-born pathogens, is still unconfirmed as a route of hepatitis C virus (HCV) transmission. Our goal was to measure HCV exposure and prevalence in noninjection drug users (NIDUs). Fifty-seven NIDUs were screened by extensive questionnaire to exclude prior injection drug use and evaluated for HCV-specific serologic and cellular immune responses. HCV-specific T-cell responses were measured using interferon-gamma (IFN-γ) enzyme-linked immunospot (ELISpot) assay with overlapping HCV peptides covering the entire HCV genome. Fifteen individuals who never used illicit drugs served as negative controls. Eleven people with no history of injecting drug use (19.3%) were HCV seropositive: seven with chronic HCV infection and four with previously resolved infection. Of 51 NIDUs with ELISpot results, HCV-specific cellular immunity was detected in 5 (9.8%). These responses were relatively weak and narrow. We did not find significant associations between HCV-specific immune responses and noninjection drug use practices. Subjects with HCV-specific immunity, however, were significantly more likely to have bought sex in the past 6 months, to have had more casual partners of the opposite sex in the last 6 months, and those partners were more likely to have ever injected drugs compared to subjects without HCV-specific immunity. In summary, we found serologic or cellular HCV-specific immune responses in 27.5% of NIDUs. Our results suggest that sexual behaviour associated with noninjection drug use might be a risk factor for HCV acquisition. Additional studies are needed to precisely determine the practices that lead to HCV exposure among this population.