What is the incubation period of Hepatitis A (Hep A)?

Hepatitis A Incubation Period

The incubation period of Hepatitis A virus (HAV) is 15 to 50 days, with an average of 28 days. 1, 2

Clinical Timeline and Infectivity

• HAV infection begins with viral replication in the liver, followed by excretion in bile and shedding in stool 1
• Peak infectivity occurs during the 2-week period before onset of jaundice or elevation of liver enzymes, when concentration of virus in stool is highest 1, 2
• Virus concentration in stool declines after jaundice appears 1
• Children can shed HAV for longer periods than adults - up to 10 weeks after onset of clinical illness 1, 2
• Infants infected as neonates may shed HAV for up to 6 months 1, 2

Age-Related Symptom Presentation

• In children younger than 6 years:

  • 70-90% of infections are asymptomatic 1, 2
  • When symptoms occur, they typically are not accompanied by jaundice 1

• In older children and adults:

  • Infection is typically symptomatic 1
  • Jaundice occurs in >70% of patients 1, 2

Clinical Manifestations

• Initial presentation often includes a 1-7 day prodromal illness with:

  • Fever, malaise, anorexia, nausea, abdominal discomfort 1
  • Dark urine (often one of the first noticeable symptoms) 1, 2
  • Clay-colored stool 2
  • Jaundice (appears within days of bilirubinuria onset) 2

• Signs and symptoms typically last <2 months, although 10-15% of symptomatic persons have prolonged or relapsing disease lasting up to 6 months 1, 2

Diagnostic Considerations

• Hepatitis A cannot be differentiated from other types of viral hepatitis based on clinical features alone 1, 2
• Diagnosis requires serologic testing to detect IgM antibody to HAV (IgM anti-HAV) 1, 2
• Serum IgM anti-HAV becomes detectable 5-10 days before onset of symptoms 1, 2
• IgM anti-HAV typically declines to undetectable levels <6 months after infection 1

Clinical Pitfalls and Caveats

• The incubation period is important for:

  • Contact tracing during outbreaks 1
  • Determining appropriate timing for post-exposure prophylaxis 3
  • Identifying the likely source of infection 1

• Understanding the incubation period is crucial when managing international adoptees and their contacts, as HAV outbreaks have been traced to asymptomatic adoptees from countries with high HAV endemicity 1

• The relatively long incubation period (average 28 days) means that by the time symptoms appear, contacts may have already been exposed during the peak infectivity period 1, 2

• Fulminant hepatitis A is rare but more common in people older than 50 years (case fatality rate reaches 1.8%) and patients with chronic liver disease 1, 2