Risk Factors and Transmission of Chronic Hepatitis C

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 the 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

• Injection drug users, including those who used drugs briefly many years ago.
  
  
• 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.
  
  
• Infants born to HCV-infected mothers.
  
  
• Health care workers who suffer needle-stick accidents.
  
  

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 usually mild and free of symptoms. The risk of maternal-infant spread rises with the amount of virus in the mother's blood and with complications of delivery such as early rupture of membranes and fetal monitoring. Breast-feeding has not been linked to spread of HCV.

Sexual Transmission

Sexual transmission of hepatitis C between monogamous partners appears to be uncommon. Surveys of spouses and monogamous sexual partners of patients with hepatitis C show that less than 5 percent are infected with HCV, and many of these have other risk factors for this infection. Spread of hepatitis C to a spouse or partner in stable, monogamous relationships occurs in less than 1 percent of partners per year. For these reasons, changes in sexual practices are not recommended for monogamous patients. Testing sexual partners for anti-HCV can help with patient counseling. People with multiple sex partners should be advised to follow safe sex practices, which should protect against hepatitis C as well as hepatitis B and HIV.

Sporadic Transmission

Sporadic transmission, when the source of infection is unknown, occurs in about 10 percent of acute hepatitis C cases and in 30 percent of chronic hepatitis C cases. These cases are usually referred to as sporadic or community-acquired infections. These infections may have come from exposure to the virus from cuts, wounds, or medical injections or procedures.

Unsafe Injection Practices

In many areas of the world, unsafe injection practices are an important and common cause of hepatitis C (and hepatitis B as well). Use of inadequately sterilized equipment, lack of disposable needles and syringes, and inadvertent contamination of medical infusions are unfortunately well-documented causes of transmission of hepatitis C. Careful attention to universal precautions and injection techniques should prevent this type of spread. In the United States, multiple-use vials are a frequent culprit in leading to nosocomial spread of hepatitis C.

The Hepatitis C Virus HCV is a small (40 to 60 nanometers in diameter), enveloped, single-stranded RNA virus of the family Flaviviridae and genus hepacivirus. Because the virus mutates rapidly, changes in the envelope proteins may help it evade the immune system. There are at least 6 major genotypes and more than 50 subtypes of HCV. The different genotypes have different geographic distributions. Genotypes 1a and 1b are the most common in the United States (about 75 percent of cases). Genotypes 2 and 3 are present in only 10 to 20 percent of patients. There is little difference in the severity of disease or outcome of patients infected with different genotypes. However, patients with genotypes 2 and 3 are more likely to respond to interferon treatment.

source: http://digestive.niddk.nih.gov/ddiseases/pubs/chronichepc/index.htm