Injection drug users: the overlooked core of the hepatitis C epidemic.

Injection drug users (IDUs) constitute the core of the hepatitis C epidemic in the developed world. Four times more prevalent than HIV infection, hepatitis C virus (HCV) has been acquired by at least 5 million Americans and an estimated 170 million people worldwide. In developed countries, people who use illegal drugs by injection are the largest group of persons with HCV infection and the group among whom most new infections occur. Viral transmission is uncontrolled among IDUs, with incidence rates ranging from 16%– 42% per year [1–4], and yet, our efforts to control this pandemic have largely ignored the population in whom its biology and epidemiology are being played out with the most devastating effects. Disease control depends on epidemiology , basic science, treatment, and prevention. In each of these spheres, work on HCV has focused on convenient popu-lations—patients who come to our clinics and offices of their own accord—rather than the more challenged and stigmatized populations in whom the epidemic continues to rage out of control. The ubiquitously quoted estimate of the number of Americans infected with HCV—4 mil-lion—was derived from the National Health and Nutrition Examination Survey, a study of the housed, noninstitution-alized, civilian population of the United States [5]. But the populations most severely affected by HCV are poorly captured by this study. Disproportionately low response rates can be expected in government surveys from persons engaged in illegal activities, disclosure of which could result in incarceration or deportation. In addition, the National Health and Nutrition Examination Survey sampling frame, by design, explicitly excluded several large groups known to have high prevalences of injection drug use and HCV infection: people who are homeless, incarcerated, hospitalized, or institutionalized. Available estimates of the sizes and HCV prevalences of these populations suggest that at least a million more Americans have been infected with HCV than estimated by the National Health and Nutrition Examination Survey data [6]. New HCV infections in persons who inject illicit drugs are probably not well-represented in official estimates of HCV incidence in the United States, either. National estimates of the number of new HCV infections—about 30,000 per year— are based on data from cases of acute HCV infection reported to health departments in the 4 US counties (recently expanded to 6) participating in the Sentinel Counties Study of Acute Viral Hepatitis [7]. The calculations rely on the estimate that 1 in 6 new infections come to medical …