How Hepatitis B is Transmitted
Hepatitis B is transmitted through percutaneous (skin puncture) or mucosal exposure to infectious blood or body fluids containing blood, with the primary routes being sexual contact, injection drug use, perinatal transmission from infected mothers, and household contact with infected persons. 1, 2
Primary Transmission Routes
Blood and Percutaneous Exposure
- Blood exposure through injection drug use is the most efficient mode of transmission, with HBV remaining viable on environmental surfaces for at least 7 days at room temperature. 2
- Needlestick injuries and contaminated medical/dental instruments in healthcare settings pose significant risk. 2
- HBV can be present on environmental surfaces at concentrations of 10²⁻³ virions/mL even without visible blood and still cause transmission. 1
Sexual Transmission
- Sexual transmission occurs efficiently in both heterosexual and homosexual contact, with risk factors including unprotected sex with infected partners and multiple partners. 2
- Only serum, semen, and saliva have been demonstrated to be infectious, though HBsAg has been detected in multiple body fluids. 1
- For sexual exposure to a person with acute hepatitis B, transmission risk is significant within 2 weeks of last sexual exposure. 3
Perinatal (Mother-to-Child) Transmission
- Perinatal transmission from infected mothers carries a 70-90% risk of chronic infection when the mother is both HBsAg and HBeAg positive without prophylaxis. 2
- For infants of women who are HBsAg positive but HBeAg negative, the risk for chronic infection is less than 10% without prophylaxis. 1
- Breastfeeding by an HBsAg-positive mother does NOT increase the risk of HBV transmission to the infant. 1, 2
- Children not infected at birth remain at risk from long-term contact with infected mothers—38% of such infants became infected by age 4 years in one study. 1
Household Contact
- Transmission occurs through sharing toothbrushes or razors, contact with exudates from dermatologic lesions, and contact with HBsAg-contaminated surfaces. 1, 2
- Transmission rates to susceptible household contacts range from 14-60%. 2
- Infants less than 12 months of age with close contact to primary caregivers who have acute HBV infection require prophylaxis. 3
Infectivity Levels
High Infectivity
- All HBsAg-positive persons are infectious, but those who are also HBeAg positive are more infectious because their blood contains high titers of HBV (typically 10⁷-10⁹ virions/mL). 1
- Blood contains the highest viral concentration and is the most infectious body fluid. 2
Body Fluids That Can Transmit HBV
- Highly infectious fluids: semen, vaginal secretions, and saliva. 2
- Potentially infectious fluids: cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid, amniotic fluid, tears, and bile. 2
Important Clinical Considerations
Environmental Stability
- HBV is comparatively stable in the environment and remains viable for more than 7 days on environmental surfaces at room temperature. 1, 2
- This environmental persistence means transmission can occur from contaminated surfaces even without direct person-to-person contact. 1
Occult Infection
- Persons with occult HBV infection (HBsAg-negative but HBV DNA-positive) can still transmit infection, though this is less common. 2
- Persons positive only for anti-HBc are unlikely to be infectious except under circumstances involving direct percutaneous exposure to substantial quantities of virus (e.g., blood transfusion or organ transplant). 1
Routes with Lower Current Risk
- Blood transfusion is now rare due to donor screening for HBsAg and viral inactivation procedures. 1, 2
- Few cases have been reported of healthcare workers transmitting infection to patients since implementation of standard universal infection control precautions. 1
- No evidence exists of transmission by casual contact in the workplace, and transmission occurs rarely in childcare settings. 1