What are the primary modes of Hepatitis B (HBV) transmission?

Hepatitis B Virus Transmission Modes

Hepatitis B virus (HBV) is primarily transmitted through percutaneous exposure to blood, sexual contact, and from mother to child during birth, with blood containing the highest concentration of virus. 1

Primary Modes of Transmission

Percutaneous/Bloodborne Transmission

• Most efficient mode of HBV transmission 2, 1
• Occurs through:
  • Injection drug use (sharing needles/equipment)
  • Needlestick injuries in healthcare settings
  • Contaminated medical or dental instruments
  • Unsafe injections
  • Organ transplantation
  • Dialysis
• HBV remains viable on environmental surfaces for at least 7 days 2
• Can transmit with HBV DNA levels as low as 10²-10³ IU/mL even without visible blood 1

Sexual Transmission

• Efficiently transmitted through sexual contact among both heterosexuals and men who have sex with men (MSM) 2
• Risk factors include:
  • Unprotected sex with an infected partner
  • Multiple sexual partners
  • History of other sexually transmitted infections
  • Anal intercourse (particularly among MSM) 2, 1

Perinatal/Mother-to-Child Transmission

• Major mode of transmission globally 3
• Primarily occurs during delivery rather than in utero 4
• 70-90% of infants born to HBsAg/HBeAg-positive mothers become chronic carriers without prophylaxis 4
• Risk of chronic infection is highest for infants infected during the perinatal period (70-90%) 5

Household/Close Contact Transmission

• Occurs through prolonged, close personal contact with infected individuals 2
• Transmission routes include:
  • Sharing personal items (toothbrushes, razors)
  • Contact with exudates from dermatologic lesions
  • Contact with HBsAg-contaminated surfaces 2
• Transmission rarely occurs in childcare settings 2

Infectious Bodily Fluids

Highly Infectious

• Blood (highest concentration of virus) 2, 1
• Semen 2, 1
• Vaginal secretions 2
• Saliva (though less infectious than blood) 2, 1

Potentially Infectious

• Cerebrospinal fluid
• Synovial fluid
• Pleural fluid
• Peritoneal fluid
• Pericardial fluid
• Amniotic fluid 2, 1

Not Efficiently Infectious (unless containing blood)

• Urine
• Feces
• Vomitus
• Nasopharyngeal washings
• Sputum
• Sweat 2
• Breast milk (HBsAg in breast milk is unlikely to lead to transmission) 2

Infectivity Factors

• All HBsAg-positive persons are infectious 2, 1
• Those who are also HBeAg-positive are more infectious due to higher viral loads (typically 10⁷-10⁹ IU/mL) 2, 1
• HBV is approximately 100 times more infectious than HIV and 10 times more infectious than HCV 1

Common Misconceptions

• HBV is NOT transmitted through:
  • Casual contact in workplace settings
  • Food or water
  • Sharing eating utensils or drinking glasses
  • Hugging, kissing, holding hands
  • Coughing or sneezing 1
• Breastfeeding is NOT contraindicated for HBV-positive mothers 2, 1

High-Risk Populations

• Men who have sex with men
• Injection drug users
• Sexual partners of infected individuals
• Infants born to infected mothers
• Household contacts of infected persons
• Healthcare workers 1
• At least 30% of reported hepatitis B cases among adults cannot be associated with an identifiable risk factor 5

Understanding these transmission routes is essential for implementing effective prevention strategies, with vaccination being the most effective preventive measure against HBV infection.