Persons likely to have chronic HCV infection include those who received a blood transfusion before 1992 and past or current IDUs. US veterans who use the Department of Veterans Affairs (VA) health-care system have a higher prevalence of HCV infection (4–35%) than the general population (about 2%) (Cheung, 2000; Dominitz et al., 2005; Groom et al., 2008; Sloan et al., 2004), so VA has established a program to test all VA patients for HCV infection and to manage HCV-positive patients clinically (Kussman, 2007). As is the case with HBV infection, most patients who have acute or chronic HCV infection are asymptomatic, and their disease remains undiagnosed (Kamal, 2008).
In the United States, most IDUs have serologic evidence of HCV infection, but the prevalence is highly variable. For example, in a study of young IDUs in four US cities, the prevalence of HCV antibody was 35% overall but varied from 14% in Chicago and 27% in Los Angeles to 51% in Baltimore and New York City (Amon et al., 2008). Prevalence is strongly associated with time engaged in risky behaviors, rising as the number of years of drug-injecting accumulates and reaching 65–90% in longer-term injectors (Hagan et al., 2008). HCV prevalence in IDUs in industrialized nations has fallen in recent years. For example, in IDUs injecting for less than 1 year, HCV prevalence fell from 46% before 1995 to 32% in a more recent period and in IDUs injecting for 5 years or more, prevalence fell from 67% before 1995 to 53% in the period after 1995 (Hagan et al., 2008). Most of the estimates of HCV incidence rates in IDUs in the United States have been between 15 and 30 per 100 person years at risk, with higher incidence found in recent-onset injectors (Garfein et al., 1998; Hagan et al., 2001, 2008; Hahn et al., 2002; Maher et al., 2006; Smyth et al., 2000; Thorpe et al., 2002).
The prevalence of HCV infection in the incarcerated population has been reported to vary from 12% to 35% (Boutwell et al., 2005; Weinbaum et al., 2003). Although some HCV transmission occurs within correctional settings (Hunt and Saab, 2009; Macalino et al., 2004), the vast majority of HCV-infected inmates became infected by injection-drug use in the community and not while incarcerated (Weinbaum et al., 2003).
Although reporting of acute HCV infection does not accurately reflect the underlying incidence in the United States, the number of acute HCV infections peaked in the late 1980s and declined throughout the 1990s (Armstrong et al., 2006; Shepard et al., 2005). The decline observed in the 1990s may reflect changes in IDUs’ behavior and practices, including greater participation in needle-exchange programs (Wasley et al., 2008). It is consistent with results of studies summarized previously that suggest that HCV seroconversion rates in IDUs have declined since 1995 (Armstrong