What are the modes of hepatitis C transmission?

How Hepatitis C is Transmitted

Hepatitis C is primarily acquired through direct blood-to-blood contact, with injection drug use currently accounting for the vast majority (68-80%) of new infections in developed countries. 1, 2

Primary Transmission Routes

Injection Drug Use (Highest Risk)

• Injection drug use is the dominant transmission route in developed countries, with 50-100% of intravenous drug users becoming infected 1, 2
• HCV is acquired more rapidly than other bloodborne viruses, with up to 90% of users infected within 5 years of starting injection drug use 2
• Transmission occurs through sharing contaminated needles, syringes, and drug preparation equipment 3
• This route accounts for 68-80% of newly acquired cases in the United States and United Kingdom 1, 2

Blood Transfusions and Organ Transplantation (Historical Risk)

• Blood transfusions were a major transmission route before 1991, but screening has virtually eliminated this risk in developed countries 1, 2
• The current risk of transfusion-transmitted HCV is less than 1 in 200,000 units in England and 0.001% per unit transfused in the United States 1
• Recipients of clotting factor concentrates before 1987 (Factor IX) or 1985 (Factor VIII) have infection rates as high as 60-90% 1

Healthcare-Related Exposures

• Needlestick injuries carry a transmission risk of approximately 1.8% (range 0-7%), which is lower than hepatitis B but still significant 1, 2
• Healthcare workers overall have no higher prevalence than the general population (1-2%) 2
• Hemodialysis patients show average anti-HCV prevalence of 10%, with some centers reporting rates exceeding 60% due to inadequate infection control 2
• Unsafe medical procedures in developing countries—including reused syringes, contaminated surgical/dental equipment, and unsafe injection practices—are major transmission routes 2

Tattooing and Body Modification

• Tattooing, body piercing, and acupuncture performed without proper sterilization are documented risk factors 1, 2
• Traditional healing practices using non-sterilized instruments have contributed to HCV spread in certain countries 1

Sexual Transmission (Low but Documented Risk)

Monogamous Relationships

• Long-term monogamous heterosexual relationships carry very low transmission risk, with only 1.5% average HCV prevalence among steady spouses and less than 5% risk overall 1, 2
• HCV has not been detected by PCR in semen, urine, stool, or vaginal secretions in some studies 1

High-Risk Sexual Behaviors

• Multiple sexual partners are the most consistently identified sexual risk factor 2
• Risk thresholds include: more than 2 partners in 6 months for acute hepatitis C, ≥5 partners/year for blood donors, and ≥10 lifetime partners in the general population 2
• High-risk practices that increase transmission include anal sex, sex with wounds or bleeding, concurrent sexually transmitted diseases (especially HIV), and male-to-male sexual contact 1, 2
• HIV coinfection appears to facilitate sexual transmission, with 11.7% seropositivity in HIV-positive homosexuals without other risk factors 1

Vertical (Mother-to-Child) Transmission

• The vertical transmission rate is 5-6% for HCV-positive, HIV-negative mothers 2
• This rate increases to 14-17% for mothers coinfected with HCV and HIV 2
• When mothers are HCV RNA-positive at delivery, the transmission rate is 4.3% (range 3.9-7.1%) 2
• The only consistent predictor of transmission is presence of HCV RNA in the mother at delivery 2
• Risk factors for increased transmission include HIV coinfection, high maternal HCV RNA levels, and female infant gender 2
• Cesarean delivery does not prevent transmission and is not recommended solely for HCV 2
• Breastfeeding transmission has not been documented and is not contraindicated unless nipples are cracked or bleeding 1, 2

Household and Other Exposures

• Household transmission can occur through sharing personal items that may contact blood, such as razors or toothbrushes 1
• HCV has been detected in saliva in some studies, though casual contact (sharing meals, eating utensils, sneezing, coughing) does not transmit the virus 1
• Family members of HCV carriers have higher prevalence than the general population, with 6-8% of family contacts testing positive in some studies 1

Important Clinical Caveats

• Approximately 40% of patients with acute hepatitis C have no identifiable risk factor, suggesting unrecognized or underreported exposures 1
• The risk of transmission depends on viral titer, size of inoculum, and route of exposure 4
• Universal screening in pregnancy is now recommended by the US Preventive Services Task Force 2