What is the mode of transmission of Hepatitis B (HB)?

How Hepatitis B is Transmitted

Hepatitis B virus (HBV) is transmitted through percutaneous (puncture through the skin) or mucosal exposure to infectious blood or body fluids containing blood. 1

Primary Routes of Transmission

Blood and Body Fluid Exposure

• Blood contains the highest concentration of virus and is the most efficient mode of transmission 1
• Only serum, semen, and saliva have been definitively demonstrated to be infectious, though HBsAg can be detected in multiple body fluids 1
• Cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid, and amniotic fluid are also considered potentially infectious 1
• Urine, feces, vomitus, sputum, and sweat are NOT efficient vehicles of transmission unless they contain blood 1

Age-Specific Transmission Patterns

For Infants and Children:

• Perinatal transmission from infected mothers is the primary source 1
  • Risk of chronic infection is 70-90% if mother is both HBsAg and HBeAg positive without postexposure prophylaxis 1
  • Risk drops to <10% if mother is HBsAg positive but HBeAg negative 1
  • Breastfeeding does NOT increase transmission risk 1
• Horizontal transmission from infected household contacts 1
  • Transmission rates to susceptible household contacts range from 14-60% 1
  • Occurs through sharing toothbrushes, contact with exudates from skin lesions, or contact with HBsAg-contaminated surfaces 1

For Adolescents and Adults:

• Sexual contact accounts for approximately 39% of new infections among heterosexuals and 24% among men who have sex with men 1
  • Risk factors include unprotected sex with infected partners, multiple partners, and history of sexually transmitted infections 1
• Injection drug use accounts for approximately 16% of new infections 1
  • Includes sharing needles and injection-preparation equipment 1

Environmental Stability

• HBV remains viable on environmental surfaces for >7 days at room temperature 1
• Can be transmitted even in the absence of visible blood at concentrations of 10²⁻³ virions/mL 1
• This environmental stability makes household transmission possible through contaminated surfaces 1

Healthcare and Other Exposures

• Percutaneous exposures including needlestick injuries in healthcare settings 1
• Contaminated medical or dental instruments, unsafe injections 1
• Organ transplantation and dialysis 1
• Blood transfusion is now rare due to donor screening and viral inactivation procedures 1

Important Clinical Caveats

Infectivity Levels

• All HBsAg-positive persons are infectious, but those who are also HBeAg positive are most infectious with blood containing 10⁷-10⁹ virions/mL 1
• Persons with occult HBV infection (HBsAg negative but HBV DNA positive) can also transmit infection 1

Settings Where Transmission Does NOT Occur

• No evidence of transmission by casual contact in the workplace 1
• Transmission occurs rarely in childcare settings 1
• Person-to-person transmission in childcare has been reported only in rare instances 1

What Does NOT Transmit HBV

• Casual social contact 1
• Sharing food or drinks (unless contaminated with blood)
• Coughing or sneezing
• Hugging or kissing (unless mucosal exposure to blood occurs)