What are the modes of hepatitis B transmission, listed in order from most common to least common?

Modes of Hepatitis B Virus Transmission

Hepatitis B virus (HBV) is primarily transmitted through percutaneous or mucosal exposure to infectious blood or body fluids containing blood, with specific routes of transmission varying in frequency from most to least common. 1

Most Common Routes of HBV Transmission

1. Percutaneous exposure to blood

   • Injection drug use (sharing needles/syringes)
   • Needlestick injuries in healthcare settings
   • Contaminated medical or dental instruments
   • Unsafe injections in healthcare settings 1, 2

2. Sexual transmission

   • Unprotected sex with an infected partner
   • Multiple sexual partners
   • History of other sexually transmitted infections
   • Particularly efficient among both heterosexuals and men who have sex with men (MSM) 1, 2

3. Perinatal (vertical) transmission

   • Mother-to-child transmission during childbirth
   • Risk is 70-90% when mothers are both HBsAg and HBeAg positive
   • Risk is <10% when mothers are HBsAg positive but HBeAg negative
   • Rarely occurs in utero 1, 3

4. Household contact transmission

   • Long-term close personal contact with infected individuals
   • Sharing personal items (toothbrushes, razors)
   • Contact with exudates from dermatologic lesions
   • Contact with HBsAg-contaminated surfaces 1

Less Common Routes of HBV Transmission

1. Transfusion of blood and blood products

   • Now rare in developed countries due to donor screening and viral inactivation procedures 1

2. Organ transplantation

   • Risk has decreased significantly with screening 1

3. Dialysis procedures

   • Risk has decreased with improved infection control practices 1

4. Child care settings

   • Rare instances of person-to-person transmission 1

Infectious Body Fluids (in order of infectivity)

1. Blood - highest concentration of virus
2. Semen - proven infectious
3. Vaginal secretions - proven infectious
4. Saliva - proven infectious but lower risk
5. Other potentially infectious fluids - cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid, and amniotic fluid 1, 2

Important Characteristics of HBV Transmission

• HBV is highly infectious - approximately 100 times more infectious than HIV and 10 times more infectious than HCV 2
• The virus remains viable on environmental surfaces for at least 7 days 1
• HBV can be transmitted even when no visible blood is present 1
• All HBsAg-positive persons are infectious, but those who are also HBeAg positive are more infectious due to higher viral loads (typically 10^7-10^9 virions/mL) 1
• HBV at concentrations of just 10^2-10^3 virions/mL can cause transmission 1
• Breastfeeding by HBsAg-positive mothers does not increase risk of transmission 1

Key Risk Factors for Transmission

• Presence of HBeAg in infected individuals (indicates high viral replication and infectivity) 1
• High HBV DNA levels in infected individuals 1, 4
• Lack of immunoprophylaxis for infants born to infected mothers 3, 4
• Unprotected sexual contact, especially with multiple partners 1, 2
• Sharing injection equipment 1

Important Caveats and Pitfalls

• Despite common misconceptions, HBV is not transmitted through:

  • Casual contact in workplace settings 1
  • Food or water
  • Sharing eating utensils or drinking glasses
  • Hugging, kissing, holding hands, coughing, or sneezing 1

• Urine, feces, vomitus, nasopharyngeal washings, sputum, and sweat are not efficient vehicles of transmission unless they contain blood 1

• A common pitfall is failing to screen pregnant women for HBsAg, which is crucial for preventing perinatal transmission through timely administration of hepatitis B vaccine and HBIG to the newborn 1, 3