High incidence of hepatitis C virus reinfection in a cohort of injecting drug users.

UNLABELLED: An estimated 170 million people worldwide carry the hepatitis C virus (HCV), and in more developed countries the prevalence and incidence of HCV is particularly high among injecting drug users (IDUs). Spontaneous clearance of HCV infection and reinfection is well recognized but the level of protection against further infection conferred by HCV infection and clearance remains uncertain. We conducted a prospective study of HCV infection in IDUs recruited in Melbourne, Australia, using a much shorter median testing interval than in previous studies. Incidences of naive infection and reinfection were calculated by the person-year method and Cox proportional hazards regression used to adjust for covariates. A significantly higher HCV incidence rate was measured in previously infected IDUs (46.8% per year) compared with HCV-naive IDUs (15.5% per year). The hazard ratio for previously infected IDUs compared to HCV-naive IDUs, after adjustment for time-dependent covariates, was 2.54 (95% confidence interval, 1.11-5.78, P > |z| < 0.05). Viral persistence after reinfection appeared similar to that following naive infection. CONCLUSION: Our data suggest that HCV infection in IDUs is more likely following prior infection and clearance than in HCV-naive individuals, implying no increased immunity against further infection. This result has important implications for the future development of an HCV vaccine.

Consecutive infections and clearances of different hepatitis C virus genotypes in an injecting drug user.

BACKGROUND: The hepatitis C virus (HCV) causes significant morbidity and mortality worldwide, and is highly prevalent among injecting drug users (IDUs). Whether initial HCV infection and clearance provides protection from reinfection has not been established, but is an important question for vaccine development. OBJECTIVE: To elucidate an unusual history of HCV infection and clearance in an IDU. STUDY DESIGN: The subject was interviewed and gave blood samples at approximately three-month intervals; all samples were tested for anti-HCV and HCV RNA, genotyped if RNA detected, and checked for mixed genotypes; phylogenetic analysis performed on the subject's and injecting partners' core HCV sequences. RESULTS: We observed consecutive infections with HCV genotypes 3a, 1a and 6l, and intervening clearances, in a young IDU over 449 days. Genotypes 1a and 6l were probably acquired from the subject's injecting partners, who had genetically related infections. CONCLUSION: This case illustrates (1) the ease with which IDUs can acquire HCV, (2) that prior HCV infection does not protect against reinfection with heterologous strains, and (3) that IDUs can clear consecutive HCV infections. Our subject's history of HCV infection and clearance offers hope for vaccine development, yet demonstrates that HCV vaccines must have cross-genotypic effectiveness.