How Hepatitis B is Transmitted
Hepatitis B virus (HBV) is transmitted through percutaneous, mucosal, or nonintact skin exposure to infectious blood or body fluids, with the primary routes being sexual contact, injection drug use, perinatal transmission from mother to infant, and household contact with infected persons. 1
Primary Transmission Routes
In Adults
- Blood exposure through injection drug use is the most efficient mode of transmission 1
- Sexual transmission occurs efficiently in both heterosexual and homosexual contact 1
In Infants and Children
- Perinatal transmission from infected mothers is the dominant route, with 70-90% risk of chronic infection when the mother is both HBsAg and HBeAg positive without prophylaxis 1
- Horizontal transmission from infected household contacts accounts for substantial childhood infections—38% of infants born to HBsAg-positive mothers who escaped perinatal infection became infected by age 4 years 1
Infectious Body Fluids
Blood contains the highest viral concentration and is the most infectious 1. However, HBV can also be transmitted through:
- Highly infectious fluids: semen, vaginal secretions, and saliva 1
- Potentially infectious fluids: cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid, amniotic fluid, tears, and bile 1
- NOT efficient for transmission (unless contaminated with blood): urine, feces, vomitus, nasopharyngeal washings, sputum, sweat, and breast milk 1
Important Transmission Characteristics
Environmental Stability
HBV remains infectious on environmental surfaces for at least 7 days at room temperature 1. The virus can be transmitted even in the absence of visible blood, as concentrations of 10²-10³ virions/mL can be present on surfaces and still cause infection 1.
Household and Interpersonal Contact
Transmission occurs through:
- Sharing toothbrushes or razors 1
- Contact with exudates from dermatologic lesions 1
- Contact with HBsAg-contaminated surfaces 1
- Transmission rates to susceptible household contacts range from 14-60% 1
Healthcare and Other Settings
- Needlestick injuries and contaminated medical/dental instruments 1
- Unsafe injections in healthcare settings 1
- Organ transplantation and dialysis 1
- Blood transfusion is now rare due to donor screening 1
- Rare person-to-person transmission in child care settings and schools 1
Critical Clinical Pitfalls
Breastfeeding is NOT a contraindication to nursing by HBsAg-positive mothers, as HBsAg in breast milk is unlikely to transmit infection 1. This is an important counseling point that should not be missed.
Persons with occult HBV infection (HBsAg-negative but HBV DNA-positive) can still transmit infection, though this is less common 1. Additionally, those with elevated HBV DNA or HBeAg positivity are most infectious 1.