How Hepatitis B is Transmitted
Hepatitis B is primarily transmitted through blood and sexual contact, with the virus spreading via percutaneous (through-the-skin) exposure, mucosal contact, or exposure through broken skin to infectious blood or body fluids 1.
Primary Transmission Routes in Adults
The two dominant modes of transmission in adults are:
- Blood exposure - particularly through injection drug use and sharing needles
- Sexual contact - efficiently transmitted among both heterosexual partners and men who have sex with men (MSM)
HBV is highly infectious and can be transmitted even when visible blood is not present, remaining viable on environmental surfaces for at least 7 days 1.
Infectious Body Fluids
High-Risk Fluids (Infectious):
- Blood (most concentrated source)
- Semen and vaginal secretions
- Saliva, tears, and bile
- Cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid, and amniotic fluid 1
Low-Risk Fluids (Not Efficient Transmission):
- Urine, feces, vomitus, nasopharyngeal washings, sputum, and sweat (unless contaminated with blood)
- Breast milk - HBsAg in breast milk is unlikely to transmit infection; breastfeeding is NOT contraindicated 1
Specific Risk Factors
For Heterosexual Transmission:
- Unprotected sex with an infected partner
- Multiple sexual partners
- History of other sexually transmitted infections 1
For MSM Transmission:
For Injection Drug Users:
- Needle sharing accounts for 25-50% of hepatitis B cases in industrialized countries 2
Other Transmission Routes
Interpersonal contact transmission can occur through:
- Sharing toothbrushes or razors
- Contact with exudates from skin lesions
- Contact with HBsAg-contaminated surfaces
- Settings like schools, child care centers, and facilities for developmentally disabled persons 1
Healthcare-related transmission (now rare due to screening):
- Contaminated medical or dental instruments
- Unsafe injections
- Needle-stick injuries
- Organ transplantation
- Dialysis
- Blood transfusion (extremely rare due to donor screening) 1, 3
Perinatal Transmission
Mother-to-infant transmission occurs during childbirth, particularly when maternal HBV DNA exceeds 200,000 IU/mL 1. This is why universal screening of pregnant women and prophylaxis for exposed infants is critical.
Important Clinical Caveats
- All HBsAg-positive persons are infectious, but those with elevated HBV DNA or positive HBeAg are most infectious 1
- Occult HBV infection (HBsAg-negative but HBV DNA-positive) can also transmit infection, though transmission rates are lower 1, 3
- The virus can be transmitted in the absence of visible blood 1
- Transmission efficiency varies significantly: percutaneous blood exposure is highly efficient, while casual contact poses minimal risk