HCV is an RNA virus of the Flaviviridae family, first cloned in 1989 by Choo and colleagues, and soon after determined to be responsible for the vast majority of non-A, non-B viral hepatitis infections (Choo et al, 1989; National Institutes of Health Consensus Development Conference Panel Statement, 2002). HCV epidemics associated with IDU have been remarkably consistent across wide geographic and social contexts. With worldwide average prevalence rates of around 80-90 percent, HCV is hyperendemic among injection drug users (Hagan et al, 2005). A recent review from the European Union reinforced this, showing that the prevalence of HCV among injection drug users from all EU countries, with the exception of Luxembourg, was between 30 and 98 percent, with incidence rates ranging from 6.2 to 39.3 per 100 person years (Roy et al., 2002). Even countries with traditionally low levels of injection drug use, such as Japan and Korea, are now experiencing epidemics of HCV among injection drug users (Satoh et al, 2004; Suh and Jeong, 2006).

Multiple studies evaluating knowledge of hepatitis transmission and prevention have been completed in at-risk populations, and show similar results: little is known about viral transmission and prevention, and HCV infection is considered non-desirable but much less threatening than HIV (Carey et al, 2005; Hagan et al, 2005; Southgate et al., 2005). Although HCV has an indolent natural history, with few symptoms for many years, nearly 80 percent will develop chronic

infections, of which a quarter will manifest as complications including liver cirrhosis and hepatocellular carcinoma (des Jarlais et al, 2005).

Inarguably, HCV is a pandemic. That said, it has received relatively little attention or funding in comparison with HIV. With few exceptions, the epidemiology of HCV, especially among injection drug users, has been estimated using either cross-sectional or retrospective study designs measuring prevalence represented by the seroprevalence of HCV antibodies (Cox et al, 2005). It is from these prevalence studies that worldwide prevalence estimates of HCV are calculated. This extrapolation of data is responsible for the potentially inaccurate worldwide estimate (Hagan et al, 2004). Several studies have demonstrated a delay between HCV exposure and infection, and diagnosis by the commonly used ELISA test for serum HCV antibodies (Beld et al., 1999; Stramer et al, 2004). These results imply that there is potential for the extremely high worldwide estimates of HCV seroprevalence rates in injection drug users to actually be considered conservative due to the delay of seroconversion. However, in 15 percent of documented HCV-infected people there is spontaneous HCV viral clearance in the absence of seroreversion (Thomas et al, 2000), and results such as these imply, in contrast, that prevalence estimates using seroprevalence of anti-HCV overestimate the true global prevalence. The main lesson to be extracted from this discrepancy is a need for further prospective studies in injection drug users, using the presence of both HCV RNA and anti-HCV which will better elucidate the true magnitude of the HCV pandemic.

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