Underestimating the Prevalence of the “Silent Epidemic”

Hepatitis C virus (HCV) infections are mostly hidden and underreported, which is why it was considered by the former United States Assistant Secretary for Health, Dr. Howard Koh, to be a “Silent Epidemic”.1 According to the 2003-2010 National Health and Nutrition Examination Survey (NHANES), it is estimated that about 3.6 million people in the United States have antibodies to HCV.2 After a closer look at some excluded populations, this is likely to be a potential underestimation, which suggests that the true prevalence may be higher. The excluded high-risk populations include people who are incarcerated, homeless, or hospitalized; nursing home residents; active-duty military personnel; and people living on Indian reservations.

Brian Edlin and colleagues conducted a systematic review of peer-reviewed literature and unpublished presentations and data to estimate the prevalence of hepatitis C in these excluded populations.2 They were able to conclude that an estimated 1.0 million (range 0.4 million to 1.8 million) people with HCV antibodies were excluded from the NHANES dataset. Estimates for the excluded population include 500,000 incarcerated people, 220,000 homeless people, 120,000 people living on Indian reservations, and 75,000 people in hospitals. Most of these people are men. The study investigators suggest that there may be additional sources of underestimation, including nonresponse bias and the underrepresentation of other excluded groups at increased risk of hepatitis C.

The Centers for Disease Control and Prevention (CDC) noted that monitoring the prevalence of viral hepatitis is limited at the state and local level, resulting in under-reporting and variable data.1 According to the CDC, the number of reported acute cases of HCV for 2013 is 2,138.3 However, the estimated actual new cases of HCV for 2013 is 29,700, with a range of 23,500 to 101,400.3 The CDC notes that the actual acute cases is estimated to be 13.9 times the number of reported cases in any year, which suggest that the number of reported cases underestimates the prevalence of HCV cases.3

Since 2010, there was an increase of 151.5% in reported cases of acute HCV infection, which is likely due to true increases in incidence and improved cases of ascertainment.1 New cases of HCV infection are predominantly comprised of young persons who are white, live in non-urban areas, have a history of injection drug use, and previously used opioid agonists such as oxycodone.1 The largest increases of acute hepatitis C from 2010 to 2013 were among people 20-29 years of age (0.75 cases in 2010 to 2.01 cases in 2013 per 100,000 population) and 30-39 years of age (0.60 cases in 2010 to 1.36 cases per 100,000 population in 2013).1 People at least 60 years of age had the lowest rate of (0.10 cases per 100,000 population) acute hepatitis C in 2013.1 Improved cases of ascertainment, funded by the CDC, was reflected in the states of Florida, Massachusetts, and New York.1 There was a significant increase of cases reported in Indiana, Kentucky, and New Jersey that occurred without any federal support for ascertainment, which suggested a true increase in incidence.1

After considering some excluded populations, the more accurate number of US residents who have been infected with hepatitis C is probably at least 4.6 million (range 3.4 million to 6.0 million).2 Of those who have been infected with hepatitis C, at least 3.5 million (range 2.5 million to 4.7 million) are currently infected.2 There may still be additional sources of potential underestimation, which suggest that the true prevalence could be even higher than the current adjusted estimate.

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