The targeted use of the Hepatitis A vaccine in the U.S. since 1995 has led to a dramatic decrease in the number of reported cases of Hepatitis A.

Epidemiology

• Incidence - >7,000 cases per year in the U.S.;  50-70% of U.S. adults have antibodies
• Transmission - fecal-oral via person-to-person contact; ingestion of contaminated food or water

Organism

• Nonenveloped RNA picornavirus
• Infects only primates
• Virus survives for extended periods in seawater, fresh water, waste water and soil
• Resistant to freezing, detergents and acids
• Lack of lipid envelope confers resistance to bile lysis
• Virus infects the hepatocytes, no propensity for chronic infection

Risk Factors

• Raw seafood
• Infected food handlers
• Day-care settings

Clinical Presentation

• Occurs sporadically or in epidemics
  • More prevalent among day-care and school-aged children
  • Usually asymptomatic or mild (fever, nausea, malaise) after incubation period of about 28 days
    • May cause fulminant liver failure in patients with immunosuppression or multiple comorbidities (chronic liver or renal disease)
    • Jaundice and dark urine
  • No chronic state, but can cause fatal hepatic failure

Treatment

• Supportive

Prevention

• Vaccination prior to school entry

Diagnosis

• Indications for testing
  • New onset of jaundice, anorexia or dark urine
  • Known exposure to hepatitis
  • Suspicion of chronic hepatitis (elevated liver enzyme)
  • Screening for acute hepatitis indicates hepatitis A infection
    • Hepatitis screening panel test includes hepatitis B core antibody IgM, hepatitis A IgM, hepatitis C antibody and hepatitis B surface antigen
• Laboratory testing
  • IgM antibodies to HAV generally appear 4 weeks after infection
    • May persist up to 4 months after onset of clinical symptoms
  • Total (IgM and IgG) antibodies indicate past infection or immunization; associated with immunity

Differential Diagnosis

• Autoimmune disease - autoimmune hepatitis, systemic lupus erythematosus (SLE)
• Viral - cytomegalovirus (CMV), Epstein-Barr virus (EBV), hepatitis B, C, D or E, herpes simplex virus, varicella zoster virus
• Reactions to drugs - acetaminophen, antiseizure medications, isoniazid (Nydrazid), oral contraceptives, rifampin (Rifadin), sulfonamides
• Reactions to toxins - alcohol, tetrachloride
• Bacterial - leptospirosis, Q fever (Coxiella burnetii), Rocky Mountain spotted fever (Rickettsia rickettsii), secondary syphilis (Treponema palladium), sepsis, typhoid fever (Rickettsia typhus) 
• Parasitic - liver trematodes, toxocariasis