Risk factors
Most people acquiring HAV infection do not have risk factors but these include:

Personal contact.
Certain occupations (for example, staff of large residential institutions, sewage workers).
Travel to high-risk areas.
Male homosexuality with multiple partners.
Intravenous drug abuse.
People with clotting factor disorders who are receiving factor VIII and factor IX concentrates.

Clinical features
The incubation period is 2-6 weeks with a mean of 4 weeks.
There is a prodrome of mild flu-like symptoms (anorexia, nausea, fatigue, malaise and joint pain) preceding the jaundice. Smokers often lose their taste for tobacco. Diarrhoea can occur, particularly in children.
Fever is not usually common.

This can progress to the icteric phase with:
Dark urine (appears first).
Pale stools (not always).
Jaundice occurring in 70-85% of adults with acute HAV infection.
Abdominal pain occurring in 40% of patients.
Itch or pruritus (usually with jaundice but can occur without).

Arthralgias and skin rash. These occur less often (lower limbs and with a vasculitic appearance).
Tender hepatomegaly, splenomegaly, and lymphadenopathy may occur.

Young children are usually asymptomatic and the likelihood of symptoms tends to increase with age.
Complete clinical recovery may take up to six months after the onset of the illness.
Anorexia, malaise, and weakness may persist for some weeks after biochemical recovery.

Differential diagnosis
Other forms of viral hepatitis
Acute HIV infection
Drugs (hypersensitivity and toxicity)
Cytomegalovirus
Hepatitis A Vaccination.

Investigations
Specific antibody tests

IgM antibody to HAV is positive with onset of symptoms (usually about 3 to 4 weeks after exposure but up to 6 weeks). The test is sensitive and specific. It remains positive for between 3 and 6 months (up to 12 months). It remains positive in relapsing hepatitis.

IgG antibody to HAV appears soon after IgM and persists for many years. In the absence of IgM it indicates past infection or vaccination rather than acute infection. IgG remains detectable for life.
Liver enzymes

Alanine aminotransferase (ALT) rises more than aspartate aminotransferase (AST) again with onset of symptoms, about 4 weeks after exposure. Levels usually return to reference ranges over several weeks but can remain elevated for months.
Alkaline phosphatase rises with ALT and AST.

Other test results

Bilirubin rises soon after rises in ALT and AST levels. Levels may be very high and remain elevated for several months. Older patients have higher bilirubin levels.
Modest falls in serum albumin level may occur.

Prothrombin time usually remains normal and estimation is necessary only in unusual cases or with complications.
Indices of low-grade haemolysis may be detected.
Mild lymphocytosis is common.
Pure red cell aplasia and pancytopenia may very rarely occur.

Imaging
Ultrasound may, rarely, be needed to exclude other diseases.

Management
Mainly supportive with treatment of symptoms (fluids, antiemetics, rest).
Avoid alcohol until liver enzymes are normal.
Admit patients with severe systemic upset or intractable vomiting for rehydration and observation.

G Mohan.