How is hepatitis C virus transmitted?

Hepatitis C Virus Transmission

Hepatitis C is transmitted primarily through direct blood-to-blood contact, with injection drug use currently accounting for the majority (60-68%) of new infections in developed countries, while unsafe medical procedures remain the dominant route in developing nations. 1, 2, 3

Primary Transmission Routes

Injection Drug Use (Highest Current Risk)

• Injection drug use is the most important current transmission route in developed countries, with 50-90% of people who inject drugs becoming infected and accounting for 68% of newly acquired cases in the United States. 2
• HCV is acquired more rapidly after initiating injection drug use compared to other bloodborne viruses, with up to 90% of users infected within 5 years of starting. 2
• This represents the greatest modifiable risk factor and accounts for the majority of ongoing transmission. 1

Blood Transfusions and Organ Transplantation (Historical Risk, Now Minimal)

• Blood transfusions and organ transplantation were major transmission routes until 1991, but donor screening has virtually eliminated this risk in developed countries, reducing transmission to 0.001% per unit transfused. 1, 2
• Clotting factor concentrates posed extremely high risk (up to 90% infection rates in hemophiliacs) until viral inactivation procedures were introduced in 1985-1987. 1
• Currently, transfusion-associated HCV is so rare that surveillance systems cannot detect cases, though risk is not zero. 1

Unsafe Medical and Injection Practices

• In developing countries, unsafe injection practices with multiple-use medication vials, reused syringes, or unsanitary medical procedures (surgery, endoscopy, dental treatment) are the main causes of HCV transmission. 2, 4
• Hemodialysis patients show average anti-HCV prevalence of 10%, with some centers reporting rates exceeding 60%, primarily due to inadequate infection control practices. 2
• Tattooing, piercing, and acupuncture without proper disinfection are documented risk factors. 2

Occupational Needlestick Injuries

• Needlestick injuries carry a transmission risk of approximately 1.8% (range 0-7%) from HCV-positive sources. 2, 5
• Despite occupational exposure, healthcare workers have no higher prevalence than the general population (1-2%). 2

Sexual Transmission (Inefficient but Documented)

Low Risk in Monogamous Relationships

• Long-term monogamous heterosexual relationships show very low transmission risk, with average HCV prevalence of only 1.5% among steady spouses. 1, 2, 6
• Sexual transmission appears to occur but the virus is inefficiently spread through this manner. 1

Higher Risk with Multiple Partners and High-Risk Practices

• Multiple sexual partners is the most consistently identified sexual risk factor, with thresholds including: 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, 6
• High-risk sexual practices including anal sex, sex with wounds, concurrent sexually transmitted diseases (especially HIV), and male-to-male sexual contact increase transmission risk. 2, 6
• Among high-risk populations, HCV prevalence averages 6% even without injection drug use history. 6

Important caveat: The low prevalence of HCV infection among long-term spouses and the lack of substantially higher rates among men who have sex with men (compared to heterosexuals) have raised questions about the importance of sexual activity in transmission. Unacknowledged percutaneous risk factors (such as illegal injecting-drug use) might contribute to increased risk among persons with high-risk sexual practices. 1

Perinatal (Mother-to-Child) Transmission

Transmission Rates

• The vertical transmission rate is 5-6% for HCV-positive, HIV-negative mothers and increases to 14-17% for HCV/HIV coinfected mothers. 1, 2
• The rate is 1.7% when mothers are anti-HCV positive regardless of RNA status, and 4.3% (range 3.9-7.1%) when mothers are HCV RNA-positive. 2

Risk Factors and Prevention

• The only consistent predictor of transmission is presence of HCV RNA in the mother at delivery. 1, 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 indication. 2
• Breastfeeding transmission has not been documented and is not contraindicated unless nipples are cracked or bleeding. 1, 2

Household Contact (Rare)

• Case-control studies have reported an association between nonsexual household contact and acquiring hepatitis C through direct or inapparent percutaneous or permucosal exposure to infectious blood. 1
• HCV transmission to nonsexual household contacts is probably uncommon in the United States. 1
• One documented case involved an HCV-infected mother transmitting HCV to her hemophilic child during home infusion therapy after an unintentional needle stick. 1

Prevention Recommendations

For All At-Risk Individuals

• Screen HCV-positive patients for other sexually transmitted infections including HIV, syphilis, gonorrhea, chlamydia, and hepatitis B. 2
• Vaccinate against hepatitis A and B viruses if not immune. 2
• Counsel patients to avoid donating blood, organs, tissues, or semen, and not to share any instruments that penetrate skin. 2

Sexual Activity Counseling

• For monogamous couples, barrier protection is not necessarily recommended given the very low transmission risk. 2
• For those with multiple partners or high-risk sexual practices, latex condoms should be used correctly and consistently. 2, 6

Pregnancy-Related

• The US Preventive Services Task Force recommends universal screening in pregnancy. 2

Critical pitfall to avoid: Do not assume sexual transmission in household contacts without carefully excluding direct percutaneous exposures, as these are far more likely routes of transmission even within families. 1, 7