Transmission

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HCV is mainly transmitted by direct blood-to-blood contact. The sharing of needles and other drug injecting equipment, such as spoons and cotton, is the most common source of infection, and HCV prevalence is very high among injecting drug users (IDUs).1,2,3 Blood-to-blood HCV transmission has also occurred through transfusions of blood or blood products, such as the clotting factors required by people with haemophilia, prior to widespread screening and sterilisation procedures for donated blood in 1992.

Any objects that come into contact with blood can potentially spread HCV, a much more resilient virus than HIV. These include unsterilised tattooing, piercing, and acupuncture equipment and shared personal items such as razors and toothbrushes.4 Used syringes may be able to transmit HCV for weeks after use. In laboratory tests, infectious virus has been found in syringes after as long as nine weeks under certain conditions.5

Healthcare workers should employ universal precautions to prevent accidental exposure to HCV while at work. Sharing straws to snort drugs is another potential means of HCV transmission, as is the sharing of spoons or other "works" used for injecting, even if sterile new needles are being used. HCV transmission rarely occurs through household contact. For about 10% of people with HCV, the route of infection is unknown.

HCV is sometimes detectable in body fluids other than blood at very low concentrations. HCV has been detected in menstrual blood, semen, vaginal and cervical secretions. It has been observed to be compartmentalised in the female genital tract. In most cases, levels of HCV in other body fluids are too low to lead to transmission. Earlier evidence had suggested that although HCV can be transmitted sexually, it was not passed on by this route very easily. More recently, there is increasing evidence of sexual transmission between men, and rare cases of heterosexual transmission have been reported.

Heterosexual transmission

Studies of long-term monogamous heterosexual partners of HCV-infected people demonstrate that sexual transmission rates are very low. Studies of HCV-serodiscordant heterosexual couples have shown that unprotected intercourse has led to zero or extremely low rates of infection after thousands of sexual acts and up to ten years of  follow-up.6,7,8 One literature review found that between 1 and 3% of heterosexual partners of HCV-infected people contract the virus.9 However, while rates may be very low, heterosexual transmission of HCV continues to be reported.

There is some evidence that people co-infected with both HIV and HCV are more likely to transmit HCV through sex, perhaps because they have higher levels of HCV in their genital fluids.10,11 However, several studies of women, including the large American Women's Interagency HIV Study (WIHS) and two studies in Cameroon and the Ivory Coast, found low rates of HCV infection in both HIV-positive and HIV-negative women.12,13,14 In the Marincovich study cited above, no instances of sexual HCV transmission were seen even among subjects co-infected with HIV.

Sexual transmission between men

Outbreaks of new HCV infections attributable to sexual transmission have been reported among gay men in a growing list of locations including London, Paris,15 16 17 the Netherlands, Australia and North America. There is also evidence that HCV is being transmitted internationally through male-male sexual contact.

Factors associated with sexual transmission of HCV between men include the presence of other sexually transmitted infections (STIs) such as syphilis or gonorrhoea, 'rough' anal sex (particularly fisting) associated with anal trauma and bleeding, and sometimes recent snorting of drugs (which could involve sharing paraphernalia for nasal drug use, a known factor in HCV transmission).18 19 20 21 22 23 Fisting has repeatedly been identified as a risk factor.24

While the exact route of infection is not yet clear, the virus appears to be transmitted mainly through blood rather than semen.25 26 Sexual practices that involve exposure to blood, such as fisting and unprotected anal intercourse, pose the largest risk of transmission. There is evidence that people who have multiple sexual partners and men who have sex with men are at higher risk for sexual transmission of HCV than monogamous heterosexual individuals.2 27 28 29 30 31 Cases of sexual transmission of HCV are seen far less frequently in HIV-negative than in HIV-positive gay men, but it is unclear if HIV infection increases the risk of acquiring HCV.

Vertical transmission

Mother-to-child transmission of HCV may occur before or during birth. Rates of mother-to-baby transmission of HCV have ranged from 4 to 10% in published studies, with an average incidence of about 6%.32 33 34 Higher blood levels of HCV, and co-infection with HIV, increase the risk: an extensive meta-analysis has found that HIV coinfection doubles the risk of HCV transmission. HIV-uninfected mothers with undetectable HCV viral load are at lowest risk of transmitting HCV.

As with HIV, HCV transmission may be more likely during birth, rather than in the womb, although one study has estimated that between a third and a half of transmissions occur late in pregnancy.35 Evidence suggests that delivery by caesarean section reduces the likelihood of transmission, but the benefits of the procedure remain controversial.36

A small amount of HCV may be present in breast milk, especially if the mother has a high HCV viral load. However, some studies have found that breastfeeding increased the risk of HCV transmission to infants while others have found no association. Consequently, current United Kingdom and United States guidelines do not discourage breastfeeding by women with HCV, except when a woman has cracked nipples or HIV co-infection.

Superinfection

Research suggests that infection with one strain of HCV does not prevent superinfection with other types. A study of young IDUs in San Francisco found that the incidence of HCV superinfection was almost as high as new initial HCV infections. While superinfection did not lead to more aggressive disease, its presence suggests that cross-protective immunity against different HCV strains may not develop, which could hamper the development of an effective HCV vaccine.37

References

  1. Hagan H et al. Sharing of drug preparation equipment as a risk factor for Hepatitis C. American J Publ Health 91: 42-46, 2001
  2. Rauch A et al. Unsafe sex and increased incidence of hepatitis C virus infection among HIV-infected men who have sex with men: the Swiss HIV Cohort Study. Clin Infect Dis 41: 395-402, 2005
  3. Sprinz E et al. Hepatitis C virus infection in a southern Brazilian cohort of HIV-infected patients. Second International AIDS Society Conference on HIV Pathogenesis and Treatment, Paris, abstract 978, 2003
  4. Haley RW et al. The tattooing paradox: Are studies of acute hepatitis adequate to identify routes of transmission of subclinical hepatitis C infection? Ann Intern Med 163: 1095-1098, 2003
  5. Paintsil E et al. Survival of HCV in syringes: implication for HCV transmission among injection drug users. Seventeenth Conference on Retroviruses and Opportunistic Infections, San Francisco, abstract 168, 2010
  6. Marincovich B et al. Absence of hepatitis C virus transmission in a prospective cohort of heterosexual serodiscordant couples. Sex Transm Infect 79: 160-162, 2003
  7. Vandelli C Lack of evidence of sexual transmission of hepatitis C among monogamous couples: results of a 10-year prospective follow-up study. Amer J Gastroenterol 5: 885-889, 2004
  8. Tahan V et al. Sexual transmission of HCV between spouses. Am J Gastroenterol 100(4): 821-824, 2005
  9. Rooney G and Gilson R Sexual transmission of hepatitis C virus infection. Sex Transm Infect 74: 399-404, 1998
  10. d'Oliveira A et al. Prevalence and sexual risk of hepatitis C virus infection when human immunodeficiency virus was acquired through sexual intercourse among patients of the Lyon University Hospitals, France, 1992-2002. J Viral Hepat 12: 330-332, 2005
  11. Pasquier C et al. Intermittent detection of hepatitis C virus (HCV) in semen from men with human immunodeficiency virus type 1 (HIV-1) and HCV. J Med Virol 69: 344-349, 2003
  12. Augenbraun M et al. Incident hepatitis C virus in women with human immunodeficiency virus infection. Clin Infect Dis 37: 1357-1364, 2003
  13. Msellati P et al. Prevalence of hepatitis B and C viruses and HCV genotypes in HIV-positive and negative pregnant women in Abidjan, Ivory Coast (West Africa). Second International AIDS Society Conference on HIV Pathogenesis and Treatment, Paris, abstract 974, 2003
  14. Njouom R et al. Seroprevalence of HCV among HIV-positive compared to HIV-negative pregnant women in Yaounde, Cameroon. Second International AIDS Society Conference on HIV Pathogenesis and Treatment, Paris, abstract 967, 2003
  15. Chaix ML et al. Phylogenetic analysis reveals a cluster of genotype 4 HCV transmitted by sexual intercourse in HIV-1 infected men. 55th Annual Meeting of the American Society for the Study of Liver Diseases, Boston, abstract 34, 2004
  16. Chaix ML et al. Homosexually transmitted HCV acute infection related to a clustered genotype 4 HCV in HIV-1-infected men and inefficacy of early antiviral therapy. Twelfth Conference on Retroviruses and Opportunistic Infections, Boston, abstract 122, 2005
  17. Ghosn J et al. Acute hepatitis C in HIV-infected men who have sex with men. HIV Med 5: 303-306, 2004
  18. Aizen K et al. Acute hepatitis C (HCV) in a cohort of HIV-positive homosexual men- patient characteristics, risk factors and outcomes. Ninth Annual Meeting of the British HIV Association, Manchester, abstract P45, 2003
  19. Bhagani S et al. Acute hepatitis C virus (HCV) in a cohort of HIV-positive men: outcomes and response to pegylated interferon-alpha2b and ribavirin. Tenth Anniversary British HIV Association Conference, Cardiff, abstract 020, 2004
  20. Browne RE et al. Increasing incidence of acute hepatitis C in HIV-positive men secondary to sexual transmission: a new epidemic? Ninth Annual Meeting of the British HIV Association, Manchester, abstract 016, 2003
  21. Gilleece Y et al. Evaluate changes in incidence and treatment of acute hepatitis C infection. Fifteenth International AIDS Conference, Bangkok, abstract 3296, 2004
  22. Lascar RM et al. Outcome of acute hepatitis C in HIV-positive homosexual men. Ninth Annual Meeting of the British HIV Association, Manchester, abstract 017, 2003
  23. Nelson M et al. Increasing incidence of acute hepatitis C in HIV positive men secondary to sexual transmission, epidemiology and treatment. Ninth European AIDS Conference, Warsaw, abstract F12/3, 2003
  24. Turner JM et al.. Behavioural predictors of subsequent hepatitis C diagnosis in a UK clinic sample of HIV-positive men who have sex with men. Sex Transm Infect 82: 298-300, 2006
  25. Schmidt AJ et al. The trouble with bleeding: why do HIV-positive gay men get hepatitis C? 12th European AIDS Conference, Cologne, BPD 1/7, 2009
  26. Turner J et al. Hepatitis C viral load in semen of HIV-positive men during acute and chronic hepatitis infection. Second joint BHIVA/BASHH Conference, Manchester. Abstract O5, 2010
  27. Abrescia N et al. Sexual transmission of HCV in sexually infected HIV women. 14th International AIDS Conference, Barcelona, abstract C11013, 2002
  28. Craib KJP et al. Evidence of sexual transmission of hepatitis C virus (HCV) in a cohort of homosexual men. Eighth Conference on Retroviruses and Opportunistic Infections, Chicago, abstract 561, 2001
  29. Mendes-Correa MCJ et al. Risk factors associated to hepatitis C infection among patients with HIV infection. Fourteenth International AIDS Conference, Barcelona, abstract ThPeC7493, 2002
  30. Weisbord JS et al. Prevalence and risk factors for hepatitis C virus infection among STD clinic clientele in Miami, Florida. Sex Transm Infect 79: 1-5, 2003
  31. Williams IT et al. Hepatitis C virus (HCV)-infected sex partners as a source for infection among persons with acute hepatitis C. Eleventh International Symposium on Viral Hepatitis and Liver Disease, Sydney, session WB5, 2003
  32. Catalano D et al. Maternal-fetal transmission of HCV. Role of HIV as a risk factor. Minerva Ginecologica 51: 117-119, 1999
  33. European Paediatric Hepatitis C Virus Network Three broad modalities in the natural history of vertically acquired hepatitis C virus infection. Clin Infect Dis 41: 45-51, 2005
  34. Hershow RC et al. Increased vertical transmission of human immunodeficiency virus from hepatitis C virus-coinfected mothers. Women and Infants Transmission Study, 1997
  35. Mok J et al. When does mother to child transmission of hepatitis C virus occur? Obstet Gynecol Surv 60: 572-574, 2005
  36. Gibb D et al. Early report: Mother-to-child transmission of hepatitis C virus: evidence for preventable peripartum transmission. Lancet 356: 904-907, 2000
  37. Herring BL et al. Frequent hepatitis C virus superinfection in injection drug users. J Infect Dis 190: 1396-1402, 2004
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