Prevention of Hepatitis A Through Active or Passive Immunization

Features of Hepatitis A

Clinical Illness

HAV, a 27-nm RNA agent classified as a picornavirus, can produce either asymptomatic infection or symptomatic infection in humans after an average incubation period of 28 days (range: 15-50 days) ⁽⁵⁾. The illness caused by HAV infection typically has an abrupt onset that can include fever, malaise, anorexia, nausea, abdominal discomfort, dark urine, and jaundice. The likelihood of having symptoms with HAV infection is related to the person's age. In children <6 years of age, most (70%) infections are asymptomatic; if illness does occur, it is not usually accompanied by jaundice ⁽⁶⁾. Among older children and adults, infection is usually symptomatic, with jaundice occurring in >70% of patients ⁽⁷⁾. Signs and symptoms usually last <2 months, although 10%-15% of persons have prolonged or relapsing disease lasting up to 6 months ⁽⁸⁾.

In persons who have either symptomatic or asymptomatic infection, HAV replicates in the liver, is excreted in bile, and is shed in the stool. Peak infectivity of infected persons occurs during the 2-week period before onset of jaundice or elevation of liver enzymes, when the concentration of virus in stool is highest ^(9,10). The concentration of virus in stool declines after jaundice appears ^(9,10). Children and infants can shed HAV for longer periods than do adults, up to several months after the onset of clinical illness ⁽¹¹⁾. Chronic shedding of HAV in feces does not occur; however, shedding may occur in persons who have relapsing illness ⁽¹²⁾.

Diagnosis

Hepatitis A cannot be differentiated from other types of viral hepatitis based on clinical or epidemiologic features alone. Serologic testing to detect IgM antibody to the capsid proteins of HAV (IgM anti-HAV) is required to confirm a diagnosis of acute HAV infection. In most persons, IgM anti-HAV becomes detectable 5-10 days after exposure and can persist for up to 6 months after infection ⁽¹³⁾. IgG anti-HAV, which appears early in the course of infection, remains detectable for the person's lifetime and confers lifelong protection against the disease ⁽¹⁴⁾. Commercial diagnostic tests are available for the detection of IgM and total (IgM and IgG) anti-HAV in serum.