Hepatitis A virus (HAV)

Hepatitis A is an acute, self-limiting infection caused by an enterically transmitted virus. Infection is uncommon in developed countries such as Australia and New Zealand, although Aboriginal and Torres Strait Islander children who are unimmunised continue to be at risk. The majority of cases are imported, occurring in returning travellers to endemic areas.

Faecal excretion of HAV is the primary source of the virus and the most important means of transmission is from person-to-person via the faecal-oral route. Hepatitis A is rarely spread by casual contact; transmission is usually limited to within families or play contacts within day care centres.

Food or water-borne epidemics of hepatitis A are uncommon in developed countries but may occur after, for example, consumption of raw or partially cooked shellfish harvested from waters contaminated with human sewage. Although HAV is present in the blood during the incubation period and early acute phase of the illness, blood transmission of hepatitis A is rare.

HAV infection may take an icteric or anicteric course. More than 90% of infections in children under five are asymptomatic, whereas about 70% of adults will develop jaundice. Patients with symptomatic HAV infection often describe a mild prodromal illness, appearing 1–7 days before the onset of dark urine. Bilirubinuria is usually followed within days by pale faeces and jaundice (see Bile pigments in urine).

After 3–4 weeks, most people feel better and have normal bilirubin and ALT. Prolonged jaundice or a relapsing pattern of abnormal LFTs can occur but ultimately resolve. Chronic infection does not occur. Fulminant hepatitis is a rare complication. Risk factors include older age and a history of chronic liver disease, especially chronic hepatitis B or C.

Hepatitis A is not more severe in pregnant women and there is no effect on fetal health or survival.

Following recovery from infection, immunity persists for life.

Acute hepatitis A cannot be distinguished from other forms of acute viral hepatitis on clinical grounds, although there may be epidemiological clues to the diagnosis. Anti-HAV IgM is detectable in >95% of patients at their first presentation and remains positive for 3–6 months.

The presence in the serum of anti-HAV IgM antibodies in adults without clinical features of viral hepatitis does not necessarily indicate acute disease. Such patients may have previous HAV infection with prolonged presence of anti-HAV IgM, a false-positive result, or asymptomatic infection (more common in children <5 years than in adults).

Anti-HAV IgG appears soon after IgM and persists for life. Anti-HAV IgG may also be detectable in infants, due to maternally-acquired antibodies or after vaccination.

Hepatitis A is a notifiable illness.