Hepatitis B Transmission Routes
Hepatitis B virus (HBV) is transmitted through percutaneous or mucosal 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 Mechanisms
Blood and Percutaneous Exposure
- Blood exposure is the most efficient mode of transmission, particularly through injection drug use and sharing of injection-preparation equipment 1, 2
- HBV remains viable on environmental surfaces for at least 7 days at room temperature, and can transmit infection even at concentrations as low as 10²-10³ IU/mL in the absence of visible blood 1
- Needlestick injuries, contaminated medical or dental instruments, unsafe injections, tattooing, and acupuncture can all transmit HBV 1
- Blood transfusion and organ transplantation are now rare sources due to donor screening, but remain possible routes 1
Sexual Transmission
- Sexual transmission occurs efficiently in both heterosexual and homosexual contact 1, 2, 3
- Risk factors include: unprotected sex with an infected partner, multiple sex partners, history of other sexually transmitted infections, and anal intercourse (particularly among men who have sex with men) 1
- Semen and vaginal secretions are infectious and contain significant viral concentrations 1
- Secondary attack rates among serosusceptible spouse contacts range from 20-27% 4
Perinatal Transmission
- For infants born to mothers who are both HBsAg-positive and HBeAg-positive, the risk of chronic infection is 70-90% without postexposure prophylaxis 1, 2
- For mothers who are HBsAg-positive but HBeAg-negative, the risk drops to <10% without prophylaxis 1
- Infants not infected at birth remain at risk, with 38% becoming infected by age 4 years through ongoing household contact 1
Household and Interpersonal Contact
- Transmission occurs through sharing personal items like toothbrushes or razors, contact with exudates from dermatologic lesions, and contact with HBsAg-contaminated surfaces 1, 2
- Transmission rates to susceptible household contacts range from 14-60% 2
- Person-to-person transmission can occur in schools, child care centers, and facilities for developmentally disabled persons, especially with aggressive behavior or open skin lesions 1
Infectious Body Fluids
Highly Infectious Fluids
- Blood contains the highest viral concentration (typically 10⁷-10⁹ IU/mL in HBeAg-positive persons) 1, 2
- Semen and saliva have been demonstrated to be infectious, though at lower concentrations than blood 1, 2
Potentially Infectious Fluids
- Cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid, amniotic fluid, tears, and bile are considered potentially infectious 1, 2
Non-Infectious or Low-Risk Fluids
- Urine, feces, vomitus, nasopharyngeal washings, sputum, and sweat are not efficient vehicles of transmission unless they contain blood 1
Critical Clinical Pitfalls
Breastfeeding Safety
- Breastfeeding by an HBsAg-positive mother is NOT a contraindication, as HBsAg in breast milk is unlikely to transmit infection and does not increase risk when proper prophylaxis is given to the infant 1, 2
Occult Infection
- Persons with occult HBV infection (HBsAg-negative but HBV DNA-positive) can still transmit infection, though less commonly than those who are HBsAg-positive 1, 2
- HBV DNA has been detected in <5% of persons with isolated anti-HBc 1