The Burden of Disease and the Evolving Landscape in Hepatitis C Therapy

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Introduction: Prevalence and Incidence

Chronic active hepatitis C is currently a leading worldwide cause of liver-related morbidity and mortality. Globally, 3% of the population, or 170 million people, are infected with this bloodborne infection,[1] including nearly 5 million in the United States, 85% of whom have chronic disease.[2-4]

Prevalence

Before measures were implemented to screen for the hepatitis C virus (HCV), thousands of individuals were exposed. Initially, US estimates of HCV prevalence were based on data obtained from the Third National Health and Nutrition Examination Survey (NHANES III) which sampled 21,000 noninstitutionalized civilian people between 1988 and 1994;[5] 1.8% of this population had antibodies to HCV and 74% had detectable HCV RNA.[5] These numbers, when projected to the entire US population, suggested that nearly 4 million individuals in the United States were infected. These data also identified demographic, ethnic, and geographic variations. Non-Hispanic blacks and men were most likely to have been exposed, and 65% of all HCV antibody-positive persons were between the ages of 30 and 49 years. It is now known that this survey of the general population severely underestimated the actual disease prevalence because it excluded several populations with known high-risk behaviors. A survey of 1032 outpatient veterans found that 18% had evidence of HCV exposure,[6] whereas in a screening of homeless veterans, 40% were found to have evidence of HCV exposure.[7] Screening in the prison systems has shown even higher rates of HCV exposure, with a prevalence of 39% among 6536 male inmates and 54% among 977 female inmates in the California correction system.[8] Although a current accurate prevalence estimate does not exist, it is likely higher than the 1.8% suggested by the NHANES data or the 1.6% estimated by a more recent 1999-2002 population survey (Table 1).[2]

Table 1. Incidence and Prevalence of HCV Infection by Specific Population[2,5,82,83]

Rate of New Cases of HCV/Year (Incidence)*

Total Population With Anti-HCV (Prevalence) 1994

Total Population With Anti-HCV (Prevalence) 2002

Most Prevalent Age Range (1994)

Most Prevalent Age Range (2002)

Metabolic Syndrome Prevalence

US: total general population

1992: 2.4/100,0002005: 0.2/100,000

1.8%

1.6%

3.9% 30-39 yrs

4.3% 40-49 yrs

21.8%

Non-Hispanic whites

****

1.5%

1.5

3.2% 30-39 yrs

3.8% 40-49 yrs

23.8%

Non-Hispanic blacks

****

3.2

3.0

6.3% 40-49 yrs

9.4% 40-49 yrs

21.6%

Hispanic

****

2.1***

1.3***

6.0% 50-59 yrs

** 50-59 yrs in men

31.9%

Male

0.26/100,000

2.5

2.1

**40-49 yrs

24%

Female

0.21/100,000

1.2

1.1

**40-49 yrs

23.4%

*2005 unless otherwise specified** Data presented in table form; prevalence not quantified in article***Peak in prevalence among Mexican Americans 50-59 years may not reflect true prevalence due to the small numbers of subjects in this age group, and also likely explains the discrepancy between the 1994 and 2002 reports****Incidence not quantified; article states no significant difference between ethnicities

Incidence

After the identification of the virus in 1989 and the recognition of potential risk factors for exposure, implementation of universal precautions, screening of blood products, and educational and needle-exchange programs led to a dramatic decrease in the incidence of hepatitis C. The Centers for Disease Control and Prevention estimates that the annual incidence of acute HCV infection has decreased from 240,000 new cases per year in the United States in the 1980s to 26,000 in 2004.[4]

This decrease in disease acquisition will unfortunately not translate to a decrease in disease burden for decades. In most individuals, the disease is clinically silent, remaining unrecognized for 20 years or more while significant hepatic injury occurs, resulting in clinical manifestations. Thus, although the prevalence of HCV infection peaked in the 1990s, the prevalence of liver disease caused by HCV is not expected to peak until after the year 2030 and to plateau around 2040.[9]