Introduction

Some modes of transmission of hepatitis C virus are well documented and widely accepted; others are less well defined and require further study. It is clear that HCV is most frequently transmitted through large or repeated direct percutaneous exposures to infected blood. The two most common exposures associated with transmission of HCV are blood transfusion and injection drug use.

Blood Transfusion/Receipt of Blood Products

Early case-control studies of patients with newly acquired, symptomatic non-A, non-B hepatitis found a significant association between disease acquisition and a history six months prior to illness of blood transfusions, injection drug use, health care employment with frequent exposure to blood, personal contact with others who had hepatitis, multiple sexual partners or low socioeconomic status.(1,2) Today, HCV is rarely transmitted by blood transfusion or transplantation of organs due to thorough screening of the blood supply for the presence of the virus and inactivation procedures that destroy bloodborne viruses. In the last several years, blood banks have instituted techniques that utilize nucleic acid amplification of the hepatitis C virus, which will detect the presence of virus even in newly-infected patients who are still hepatitis C antibody-negative. These techniques are estimated to have prevented 56 transfusion-associated HCV infections per year in the U.S. since 1999, and have lowered the current risk of acquiring HCV via transfused blood products to 1 in 2 million.(3)

Injection Drug Use

Injection drug use has been the principal mode of transmission of HCV since the 1970's. In comparison to other viral infections, HCV is more rapidly acquired after initiation of intravenous drug use.(4) In addition, rates of HCV among young injecting drug-users are four times higher than HIV infection.(5) Studies of injection drug users have demonstrated that the prevalence of HCV infection in them is extremely high, with up to 90% having been exposed.(6) In addition, the incidence of new infections is also high, with seroconversion rates of 10-20 percent per year of injecting.(7,8) Duration of injecting is the strongest single predictor of risk of HCV infection among injection drug users.(9)

Sexual Transmission

The topic of sexual transmission of HCV has been controversial. It is believed that HCV can be transmitted sexually, but that it is inefficient -- meaning, it is not easy or likely to pass the virus during sex. On the other hand, HCV infection is very efficient when it is passed from the blood of one person to the blood of another person, such as when people share needles for drug use. The frequency of HCV transmission between monogamous sex partners is very low according to most studies. However, the likelihood of sexual transmission of HCV is increased under any of the following circumstances:

• Having multiple lifetime sex partners
• Engaging in rough sex such as anal sex
• Having a history of a sexually transmitted disease
• Having HIV
• Having sex with a prostitute or intravenous drug user
• Having sex during menstruation or whenever blood is present

When counseling patients regarding sexual transmission, the following issues may be relevant:

• For discordant couples, with one HCV-positive partner and one HCV-negative partner, the negative partner should be regularly screened for HCV infection.
• For discordant couples in long-term monogamous relationships, a change in sexual practices is not necessary (e.g., if they have not been using condoms, they do not have to start using condoms).
• For patients who have new or multiple partners, HIV infection, or high-risk sexual behaviors, it is recommended that they use condoms and exercise caution regarding potential blood exposure to help reduce the chance of HCV infection.
• For HCV-negative patients who have a new HCV-positive partner or engage in high-risk behaviors with a partner of unknown HCV status, regular screening is recommended.

Other Modes of Transmission

Household Transmission

The prevalence of HCV among household contacts of people with HCV infection is low. Care providers need only advise patients to take "common sense" precautions such as not sharing items that may have blood on them (e.g., razorblades, toothbrushes) and properly covering open cuts or wounds.

The study of HCV transmission among household contacts is complicated by the difficulty of ruling out other possible modes of acquisition.

Occupational Exposures

Health care workers who have exposure to blood are at risk of infection with HCV and other bloodborne pathogens. The prevalence of HCV infection, however, is no greater in health care workers, including surgeons, than for the general population. According to the CDC, the average rate of anti-HCV seroconversion after unintentional needlesticks or sharps exposure from an HCV-positive source is 1.8% (range 0%-7%). An Italian study of 4,403 needlesticks among healthcare workers found 14 seroconversions (0.31%).(10) There is an emerging body of literature, however, that close follow-up of health care workers after a needlestick from a patient with chronic HCV, with early interferon and ribavirin therapy for the healthcare worker if they develop HCV viremia but fail to clear within 3-6 months, can be a beneficial management strategy.(11)

No Identifiable Source of Infection

According to the Centers for Disease Control and Prevention, injection drug use accounts for approximately 60% of all HCV infections in the United States, while other known exposures account for 20-30%.(5) Approximately 10% of patients in most epidemiological studies, however, have no identifiable source of infection.(12) HCV exposure in these patients may be from a number of uncommon modes of transmission, including vertical transmission, and parenteral transmission from medical or dental procedures prior to the availability of HCV testing. There are no conclusive data to show that persons with a history of exposures such as intranasal cocaine use, tattooing or body piercing are at an increased risk for HCV infection based on these exposures solely. It is believed, however, that these are potential modes of HCV acquisition in the absence of adequate sterilization techniques.

References

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2. Alter MJ, et al. Importance of heterosexual activity in the transmission of hepatitis B and non-A, non-B hepatitis. JAMA 1989;262:1201-1205.
3. Stramer SL, et al. Detection of HIV-1 and HCV infections among antibody-negative blood donors by nucleic acid-amplification testing. N Engl J Med 2004;351:760-768.
4. Garfein RS, et al. Viral infections in short-term injection drug users: the prevalence of the hepatitis C, hepatitis B, human immunodeficiency, and human T-lymphotropic viruses.. Am J Public Health 1996; 86:655-671.
5. Centers for Disease Control and Prevention. Recommendations for prevention and control of hepatitis C virus (HCV) infection and HCV-related chronic disease. MMWR 1998;47(RR-19):1-39.
6. Patrick DM et al. Public health and hepatitis C. Can J Public Health 2000;91(suppl 1):S18-S23.
7. Hahn JA, et al. Hepatitis C virus infection and needle exchange use among young injection drug users in San Francisco. Hepatology 2001;34:180-187.
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11. Sulkowski MS, Ray SC, Thomas DL. Needlestick transmission of hepatitis C. JAMA 2002;287:2406-2413.
12. Flamm SL, Parker RA, Chopra S. Risk factors associated with chronic hepatitis C virus infection: limited frequency of an unidentified source of transmission. Am J Gastroenterol 1998;93:597-600.