Explain hepatitis B infection, transmission, diagnosis, and management.

Understanding Hepatitis B

What is Hepatitis B?

Hepatitis B is a DNA virus that infects the liver through blood and body fluid exposure, causing both acute and chronic infection that can lead to cirrhosis, liver cancer, and death in 15-25% of chronically infected persons. 1 The virus infects over 2 billion people worldwide, with 360 million chronically infected and approximately 600,000 deaths annually from HBV-related liver disease or hepatocellular carcinoma. 2

Transmission Routes

HBV transmits primarily through sexual contact, percutaneous blood exposure (injection drug use, needlestick injuries), perinatal transmission from infected mothers, and prolonged household contact. 1, 3

Infectious Body Fluids (Ranked by Viral Concentration):

• Blood contains the highest viral concentration (10^7-10^9 virions/mL in highly infectious individuals) and is the most infectious 4, 3
• Semen and vaginal secretions are highly infectious 1, 4
• Saliva contains HBV but at much lower concentrations; while theoretically infectious, no documented transmission has occurred through oral mucous membrane exposure alone (except through human bites) 4
• Other potentially infectious fluids include cerebrospinal, synovial, pleural, peritoneal, pericardial, and amniotic fluid 3

Critical Environmental Persistence:

HBV remains viable and infectious on environmental surfaces for at least 7 days at room temperature, even without visible blood. 1, 4, 3 This explains household transmission through shared toothbrushes, razors, or contact with contaminated surfaces. 1, 3

Age-Dependent Transmission Risk:

• Perinatal transmission: 70-90% risk of chronic infection when mother is HBsAg and HBeAg positive without prophylaxis 3, 5
• Children <5 years: 20-50% develop chronic infection 1, 5
• Adults: <10% develop chronic infection after acute exposure 1, 5

What Does NOT Transmit HBV:

HBV is not spread by breastfeeding, kissing, hugging, coughing, ingesting food or water, sharing eating utensils or drinking glasses, or casual touching. 1 Breastfeeding by HBsAg-positive mothers is safe when infants receive appropriate postexposure prophylaxis. 4, 3

Diagnosis

Serologic Markers for Acute vs. Chronic Infection:

Acute HBV infection is diagnosed through detection of HBsAg with IgM anti-HBc in persons with clinical acute hepatitis or epidemiologic links to infected persons. 1 The incubation period is 1-4 months, with symptoms developing in only 10% of infected children <4 years but 30% of adults >30 years. 1

Chronic HBV infection is defined by persistence of HBsAg beyond 6 months. 1 In chronic infection:

• HBsAg and HBV DNA persist in blood 1
• Anti-HBc (total) remains positive 1
• Anti-HBs is absent (its presence indicates recovery or vaccination) 1

HBeAg Status and Disease Activity:

HBeAg-positive patients typically have high HBV DNA levels (10^6-10^10 IU/mL) indicating active viral replication, while HBeAg-negative/anti-HBe-positive patients generally have lower HBV DNA levels (0-10^5 IU/mL). 1 However, HBeAg-negative chronic hepatitis B can still have active inflammation and requires monitoring. 1

Isolated Anti-HBc:

When only total anti-HBc is detected, this represents: (1) resolved infection with waned anti-HBs (most common in high-prevalence populations), (2) occult chronic infection with undetectable HBsAg (<5% have detectable HBV DNA), or (3) false-positive result. 1 These persons are generally not infectious except in direct percutaneous exposures like blood transfusion or organ transplant. 1

Initial Evaluation of Chronic HBV:

All persons with chronic HBV infection require assessment of HBeAg, anti-HBe, HBV DNA levels, complete blood count, liver panel (ALT/AST), and testing for HIV, HCV, HDV, and HAV antibody. 1 Baseline alpha-fetoprotein (AFP) and ultrasound are indicated for those at HCC risk (Asian men >40 years, Asian women >50 years, persons with cirrhosis, family history of HCC, Africans >20 years). 1

Management

Immediate Actions for Diagnosed Patients:

All HBsAg-positive persons must be evaluated by a physician experienced in chronic liver disease management, as 15-25% face premature death from cirrhosis and liver cancer. 1

Contact Management and Vaccination:

Healthcare providers must encourage patients to notify sex partners, household members, and injection-drug-sharing contacts for immediate testing and vaccination. 1 The best screening test for contacts is total anti-HBc, with vaccination initiated immediately if susceptible. 6 Vaccination provides 95% protection and should continue even while awaiting test results. 6

Prevention Counseling for HBsAg-Positive Persons:

To prevent transmission, patients must:

• Use condoms with nonimmune sex partners until vaccination and immunity are documented 1, 6
• Cover all cuts and skin lesions 1
• Clean blood spills with bleach solution 1
• Refrain from donating blood, plasma, tissue, or semen 1
• Not share toothbrushes, razors, or injection equipment 1, 6
• Ensure newborns receive hepatitis B vaccine and HBIG at birth 1

To protect liver health, patients must:

• Avoid or limit alcohol consumption (refer for alcohol abuse treatment if needed) 1
• Receive hepatitis A vaccination (2 doses, 6-18 months apart) if chronic liver disease is present 1
• Undergo serial ALT/AST monitoring for progression to active hepatitis 6

Common Pitfall:

Even with low viral load and HBeAg-negative status, patients remain potentially infectious until their partners develop vaccine-induced immunity. 6 The seroprevalence of HBV among susceptible heterosexual spouses ranges from 25-59% over time, emphasizing the critical importance of partner vaccination. 6

Antiviral Therapy Considerations:

Evaluation for antiviral therapy requires assessment of HBV replication level (HBV DNA), liver injury (ALT/AST), and when indicated, liver biopsy for histologic activity and fibrosis scoring. 1 Treatment decisions should be made by specialists experienced in hepatitis B management. 1

HCC Surveillance:

Persons at high risk require ongoing surveillance with AFP and ultrasound, as HBV can cause HCC even without underlying cirrhosis through direct oncogenic mechanisms involving the HBx protein. 1, 7