Hepatitis C Virus Infection in the United States, 1999 through 2002

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The summary below is from the full report titled "The Prevalence of Hepatitis C Virus Infection in the United States, 1999 through 2002." It is in the 16 May 2006 issue of Annals of Internal Medicine (volume 144, pages 705-714). The authors are G.L. Armstrong, A. Wasley, E.P. Simard, G.M. McQuillan, W.L. Kuhnert, and M.J. Alter.

What is the problem and what is known about it so far?

Hepatitis C is the most common bloodborne infection in the United States. It is caused by the hepatitis C virus (HCV), which produces inflammation of the liver. New HCV infections can cause acute liver abnormalities, which resolve in some patients without treatment. In others, infection becomes chronic and may remain active for the rest of the person's life. Chronic HCV infection often causes no symptoms even though progressive liver damage is occurring. People chronically infected with HCV may develop liver failure, severe scarring of the liver (cirrhosis), or liver cancer. Currently, infection is most commonly transmitted by injection drug use. It can also be transmitted by having unprotected sex with an infected person. Before 1992 (when widespread screening of donated blood for infection began), the virus was also transmitted by transfusions. The Third National Health and Nutrition Examination Survey (NHANES III), a nationwide health survey performed from 1988 to 1994, indicated that about 3.9 million people (1.8% of the U.S. population) were infected with HCV.

Why did the researchers do this particular study?

To find out if, during the past decade, there had been any change in the characteristics of people being infected with HCV or in the patterns of infection in the United States.

Who was studied?

15,079 people who took part in a new NHANES survey from 1999 to 2002 and who provided blood samples for analysis.

How was the study done?

Participants were representative of the U.S. population. In addition to collecting information such as the participant's age, race, and ethnicity, the researchers collected blood samples and interviewed each participant to find out about sexual practices and illicit drug use. Blood samples were tested for evidence of past or present HCV infection.

What did the researchers find?

1.6% of the population had been infected with HCV, and about 80% of them had chronic active infection. Men had higher infection rates than women. Non-Hispanic black men between 40 and 49 years of age had the highest rate of infection. Infection rates were lower in participants younger than 40 years of age, and in this group there was no difference in likelihood of infection between black and white persons. The rate of infection was also lower in participants older than 49 years of age than in those 40 to 49 years of age. Infection was most strongly related to injection drug use in younger participants and to a history of blood transfusion before 1992 in older participants.

What are the limitations of the study?

Homeless people and people in jail were not included in the study even though these groups are known to have a high level of HCV infection.

What are the implications of the study?

Over the past decade, the overall rate of HCV infection has remained about the same. However, since Americans born between the late 1940s and the early 1960s have the highest rate of chronic infection, they are now reaching the age at which such complications as liver failure, cirrhosis, and liver cancer will become more prevalent.