What are the primary and secondary transmission routes of hepatitis B virus and the recommended prevention measures?

Hepatitis B Transmission Routes and Prevention

Hepatitis B virus is transmitted primarily through percutaneous exposure to blood (especially injection drug use) and sexual contact in adults, while perinatal transmission from infected mothers to infants represents the most critical route for chronic infection development. 1

Primary Transmission Routes

Blood Exposure (Most Efficient)

• Injection drug use is the most efficient mode of transmission due to direct percutaneous blood exposure 2
• Needlestick injuries in healthcare settings carry significant risk 1, 2
• Contaminated medical or dental instruments, unsafe injections, and dialysis equipment can transmit HBV 1
• Blood transfusion is now rare due to donor screening but remains a theoretical risk 1

Sexual Transmission (Highly Efficient)

• Sexual contact transmits HBV efficiently in both heterosexual and homosexual encounters 1, 2
• Risk factors for heterosexuals include: unprotected sex with infected partners, multiple partners, and history of other STIs 1
• Risk factors for MSM include: multiple sex partners, history of STIs, and anal intercourse 1

Perinatal Transmission (Highest Risk for Chronic Infection)

• Transmission from HBsAg-positive mothers carries a 70-90% risk of chronic infection when the mother is also HBeAg-positive without prophylaxis 2
• This route is the dominant cause of chronic HBV infection globally due to the high chronicity rate in infants 2

Household and Interpersonal Contact

• Transmission occurs through sharing toothbrushes or razors 1, 2
• Contact with exudates from dermatologic lesions 1, 2
• Contact with HBsAg-contaminated surfaces (virus remains infectious for at least 7 days) 1, 2
• Transmission rates to susceptible household contacts range from 14-60% 2

Infectious Body Fluids

Highly Infectious (Efficient Transmission)

• Blood contains the highest viral concentration 1, 2
• Semen and vaginal secretions 1, 2

Potentially Infectious (Less Efficient)

• Cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, pericardial fluid, and amniotic fluid 1, 2
• Saliva, tears, and bile (detectable but less efficient) 1

NOT Efficient Transmission Vehicles

• Urine, feces, vomitus, nasopharyngeal washings, sputum, and sweat do NOT efficiently transmit HBV unless they contain blood 1
• Breast milk is NOT a contraindication to breastfeeding as HBsAg in breast milk is unlikely to transmit infection 1, 2

Critical Environmental Characteristics

• HBV is highly infectious and can be transmitted in the absence of visible blood 1
• The virus remains infectious on environmental surfaces for at least 7 days at room temperature 1, 2
• All HBsAg-positive persons are infectious, but those with elevated HBV DNA or HBeAg are most infectious 1

Important Pitfall

• Persons with occult HBV infection (HBsAg-negative but HBV DNA-positive) can still transmit infection, though less commonly 1, 2

Comprehensive Prevention Strategy (ACIP Recommendations)

Perinatal Prevention

• Screen all pregnant women for HBsAg 1
• Test HBsAg-positive pregnant women for HBV DNA; consider maternal antiviral therapy when HBV DNA >200,000 IU/mL 1
• Administer both HepB vaccine and HBIG to infants born to HBsAg-positive mothers within 12 hours of birth (efficacy decreases markedly after 48 hours) 1, 3
• Universal vaccination of all infants beginning at birth (within 24 hours for medically stable infants ≥2,000 grams) as a safeguard for infants born to unidentified HBV-infected mothers 1

Vaccination Strategy

• Routine vaccination of all previously unvaccinated children aged <19 years 1
• Vaccination of adults at risk for HBV infection, including those requesting protection without acknowledgment of a specific risk factor 1

Post-Exposure Prophylaxis

• For percutaneous, ocular, or mucous membrane exposure to HBsAg-positive blood: administer HBIG 0.06 mL/kg IM as soon as possible and within 24 hours 3
• Value of HBIG beyond 7 days of exposure is unclear 3
• For sexual exposure to HBsAg-positive person: administer HBIG (0.06 mL/kg) within 14 days of last sexual contact and begin HepB vaccine series 3

Transmission Prevention for Infected Individuals

• Vaccinate all sexual and household contacts 4
• Use barrier protection (condoms) with non-immune partners 4
• Do NOT share personal items that might have blood contact (toothbrushes, razors) 4
• Cover open cuts and scratches 4
• Clean blood spills with detergent or bleach solution 4
• Do NOT donate blood, plasma, organs, tissue, or semen 4

What Does NOT Require Special Precautions

• HBV is NOT spread by breastfeeding, kissing, hugging, coughing, sharing food/utensils/drinking glasses, or casual touching 4
• Children with HBV can participate in all activities including contact sports and should NOT be excluded from daycare or school 4