Acute Hepatitis B

Acute hepatitis B is self-limited necroinflammatory liver injury within 6 months of infection with hepatitis B virus (HBV), a partially double-stranded DNA hepadnavirus.

• Transmission: perinatal (the major route in sub-Saharan Africa), horizontal in early childhood, sexual, parenteral (needle sharing, unsafe injections, transfusion, tattooing), healthcare-associated needlestick.
• Incubation is 45 to 180 days (average 90).
• Outcome depends on age: chronicity in 90 percent of infants infected perinatally, 25 to 50 percent of children aged 1 to 5 years, and below 5 percent of adults.

Most (70 percent) of adults have subclinical or anicteric disease; children are usually asymptomatic.

• Prodrome (1 to 2 weeks): malaise, anorexia, nausea, low grade fever, myalgia, arthralgia, urticaria (serum sickness-like), taste changes.
• Icteric phase (2 to 12 weeks): dark urine, pale stool, jaundice, right upper quadrant pain, tender hepatomegaly, itching.
• Convalescence: gradual recovery over 1 to 3 months.
• Differential diagnosis: hepatitis A, C, D and E, Epstein-Barr virus, cytomegalovirus, drug-induced liver injury, alcoholic hepatitis, autoimmune hepatitis, leptospirosis, malaria, yellow fever, biliary obstruction, ischaemic hepatitis, Wilson disease.
• Complications: acute liver failure (0.5 to 1 percent; higher with hepatitis D coinfection and reactivation), cholestatic hepatitis, prolonged illness, chronic infection, extrahepatic manifestations (serum sickness, polyarteritis nodosa, membranous glomerulonephritis, cryoglobulinaemia, aplastic anaemia), and later hepatocellular carcinoma.

Hepatitis B surface antigen (HBsAg) positive and IgM antibody to hepatitis B core antigen (anti-HBc IgM) positive confirm acute infection; HBsAg may be negative in the window period when IgM anti-HBc is the only marker.

• Alanine aminotransferase usually above 1000 IU/L, bilirubin raised, HBV DNA high, HBeAg positive in early disease.
• Prothrombin time/INR and albumin (liver synthetic function), full blood count, glucose, creatinine.
• Exclude coinfection: HIV, hepatitis C antibody, hepatitis D antibody, hepatitis A IgM, hepatitis E IgM.
• Recovery: loss of HBsAg and appearance of anti-HBs and anti-HBc IgG; failure to clear HBsAg after 6 months defines chronic infection.
• Ultrasound if jaundice or pain to exclude obstruction.

Supportive

• Outpatient care for most; rest as tolerated, hydration, small frequent meals, avoid alcohol and hepatotoxic drugs; paracetamol up to 2 g daily if needed.
• Admit if INR above 1.5, encephalopathy, vomiting with dehydration, bilirubin above 250 micromol/L, coagulopathy, pregnancy or immunosuppression.
• Monitor ALT, bilirubin and INR 1 to 2 times weekly until improving.

Pharmacological

• Antiviral therapy is not needed for uncomplicated acute infection.
• Treat severe acute hepatitis (INR above 1.5, prolonged jaundice over 4 weeks, or acute liver failure), immunosuppressed patients and fulminant cases with tenofovir disoproxil fumarate 300 mg daily or entecavir 0.5 mg daily until HBsAg clearance (and for at least 3 months after seroconversion).
• Acute liver failure: intensive care, N-acetylcysteine (150 mg/kg over 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours), lactulose 30 mL every 6 to 8 hours for encephalopathy, mannitol 0.5 g/kg for cerebral oedema, vitamin K 10 mg IV, and urgent transplant referral.
• Pruritus: cholestyramine 4 g up to three times daily.

Prevention and contacts:

• Household and sexual contacts: HBV vaccine at 0, 1 and 6 months (20 microgram adults, 10 microgram children).
• Post-exposure prophylaxis for non-immune exposed people: hepatitis B immunoglobulin 0.06 mL/kg (about 500 IU) IM within 24 to 72 hours (up to 7 days) plus vaccine dose started at the same time.
• Newborn of HBsAg-positive mother: hepatitis B immunoglobulin 100 to 200 IU IM and the first vaccine dose within 12 hours of birth, then doses at 6 and 14 weeks (or 1 and 6 months). Maternal tenofovir 300 mg daily from 28 to 32 weeks if HBV DNA above 200,000 IU/mL or HBeAg positive.

Special groups: pregnancy (monitor, tenofovir if severe), HIV (use a tenofovir-containing antiretroviral regimen), health workers (vaccine and immunity checks), children (vaccine schedule).

Red flags: encephalopathy, INR above 1.5, hypoglycaemia, rapidly falling transaminases with rising bilirubin, ascites, hepatorenal syndrome.

Follow-up: HBsAg, ALT and HBV DNA at 3 and 6 months; anti-HBs to confirm immunity; refer to hepatology if HBsAg persists beyond 6 months.