text: what hepatitis c?   heptitis c is a disease of the liver, the hepatitis c virus (hcv) is one of the most important causes of chronic liver disease in the united states. it accounts for about 20 percent of acute viral hepatitis, 60 to 70 percent of chronic hepatitis, and 30 percent of cirrhosis, end-stage liver disease, and liver cancer. almost 4 million americans, or 1.8 percent of the u.s. population, have antibody to hcv (anti-hcv), indicating ongoing or previous infection with the virus. hepatitis c causes an estimated 8,000 to 10,000 deaths annually in the united states.  a distinct and major characteristic of hepatitis c is its tendency to cause chronic liver disease. at least 75 percent of patients with acute hepatitis c ultimately develop chronic infection, and most of these patients have accompanying chronic liver disease.  chronic hepatitis c varies greatly in its course and outcome. at one end of the spectrum are patients who have no signs or symptoms of liver disease and completely normal levels of serum liver enzymes. liver biopsy usually shows some degree of chronic hepatitis, but the degree of injury is usually mild, and the overall prognosis may be good. at the other end of the spectrum are patients with severe hepatitis c who have symptoms, hcv rna in serum, and elevated serum liver enzymes, and who ultimately develop cirrhosis and end-stage liver disease. in the middle of the spectrum are many patients who have few or no symptoms, mild to moderate elevations in liver enzymes, and an uncertain prognosis. researchers estimate that at least 20 percent of patients with chronic hepatitis c develop cirrhosis, a process that takes 10 to 20 years. after 20 to 40 years, a smaller percentage of patients with chronic disease develop liver cancer.  chronic hepatitis c can cause cirrhosis, liver failure, and liver cancer. about 20 percent of patients develop cirrhosis within 10 to 20 years of the onset of infection. liver failure from chronic hepatitis c is one of the most common reasons for liver transplants in the united states. hepatitis c might be the most common cause of primary liver cancer in the developed world. in italy, spain, and japan, at least half of liver cancers could be related to hcv. men, alcoholics, patients with cirrhosis, people over age 40, and those infected for 20 to 40 years are more likely to develop hcv-related liver cancer.  risk factors and transmission  hcv is spread primarily by contact with blood and blood products. blood transfusions and the use of shared, unsterilized, or poorly sterilized needles and syringes have been the main causes of the spread of hcv in the united states. with the introduction in 1991 of routine blood screening for hcv antibody and improvements in the test in mid-1992, transfusion-related hepatitis c has virtually disappeared. at present, injection drug use is the most common risk factor for contracting the disease. however, many patients acquire hepatitis c without any known exposure to blood or to drug use.  the major high-risk groups for hepatitis c are:  people who had blood transfusions before june 1992, when sensitive tests for anti-hcv were introduced for blood screening.  people who have frequent exposure to blood products. these include patients with hemophilia, solid-organ transplants, chronic renal failure, or cancer requiring chemotherapy.  health care workers who suffer needle-stick accidents  injection drug users, including those who used drugs briefly many years ago  infants born to hcv-infected mothers  other groups who appear to be at slightly increased risk for hepatitis c are:  people with high-risk sexual behavior, multiple partners, and sexually transmitted diseases  people who use cocaine, particularly with intranasal administration, using shared equipment  maternal-infant transmission  maternal-infant transmission is not common. in most studies, only 5 percent of infants born to infected women become infected. the disease in newborns is u