Background:  The transmission of hepatitis C virus (HCV) and human immunodeficiency virus (HIV) among injection drug users (IDU) is associated with the sharing of equipment used to prepare and administer drugs. The prevalence of HCV among IDU exceeds that of HIV across all seroprevalence studies. We hypothesized that the high prevalence of HCV among IDU may be due to the ability of the virus to remain viable in contaminated syringes for prolonged periods.
Methods:  We developed a microculture assay using a genotype 2a reporter virus to examine the viability of HCV in microliter volumes of residual blood within contaminated syringes.  Syringes were loaded with HCV-spiked blood to replicate the practice of "booting" by IDU. We stimulated 2 scenarios of residual volumes after complete depression of the plunger; low (2 µL) and high (32 µL) with 1-cc insulin syringe (with permanently attached needle) and 1-cc tuberculin syringe (with detachable needle), respectively. Syringes were either immediately tested for viable virus or stored at room temperature, 37ºC, and 4ºC for up to 56 days before testing. Virus was recovered from stored syringes and tested for infectivity in cell culture.  Relative luciferase activity was a function of HCV infectivity

Results:  We observed a biphasic rate of decay (t_½α = 0.4h and t_½β = 28h) of the virus at room temperature. HCV infectivity was not detected in syringes loaded with 2 µl (ie, insulin syringe) beyond day one at all storage temperatures except for the syringes stored at 4º that remained viable (5% of syringes) up to Day 7. After 7 days of storage, the percentage of 32 µL syringes that were positive was 96 ± 7.5, 71± 23.1, and 52 ± 20 at 4º, room temperature, and 37º, respectively. For syringes loaded with 32 µL of HCV-spiked blood, viable virus was recovered up to day 56. In general, the infectivity of the recovered virus was inversely related to duration and temperature of storage.

Conclusions:  The high prevalence of HCV among IDU may be partly due to the resilience of the virus and the type of syringe (ie, size and design) in circulation. Our findings may be used to guide prevention strategies.