Hepatitis A

Hepatitis A is an acute, self limiting viral infection of the liver caused by hepatitis A virus, a non enveloped ribonucleic acid picornavirus. It is transmitted predominantly via the faecal oral route through contaminated food or water or close person to person contact.

Severity of illness is closely related to age at infection. There is no chronic carrier state or progression to chronic liver disease, which distinguishes it from hepatitis B and hepatitis C.

Pathophysiology and epidemiology

• Following ingestion, the virus replicates within hepatocytes.
• Liver injury is believed to result predominantly from the host immune response to infected hepatocytes rather than direct viral cytopathic effect, explaining the immunologically mediated nature of the hepatitis.
• Infection confers lifelong immunity.
• Severity of clinical illness increases markedly with age at first infection. The large majority of infections in young children under six years are asymptomatic or very mild, while older children and adults are far more likely to develop overt, symptomatic icteric hepatitis.

• A prodromal phase of fatigue, malaise, nausea, anorexia, low grade fever and right upper quadrant discomfort precedes the onset of jaundice by several days to a week, with the onset of jaundice frequently accompanied by improvement in the preceding constitutional symptoms.
• Jaundice, dark urine and pale stools characterise the icteric phase, present in the majority of symptomatic adult presentations though notably absent in most young children with the infection, who more typically present with a mild, non specific, often unrecognised illness.
• The overall illness is generally self limiting, with symptoms and liver enzyme abnormalities resolving over several weeks to, occasionally, a few months, without progression to chronic liver disease.
• Fulminant hepatic failure, presenting with worsening jaundice, coagulopathy (rising international normalised ratio) and hepatic encephalopathy, is a rare but serious complication, occurring more frequently in older adults and those with pre-existing chronic liver disease, and represents a medical emergency requiring urgent specialist liver assessment.

• Hepatitis A specific immunoglobulin M antibody testing confirms acute infection. It becomes detectable around the time of symptom onset and generally persists for three to six months.
• Hepatitis A immunoglobulin G indicates past infection or prior vaccination and confers lifelong immunity.
• Liver function tests typically show markedly elevated transaminases, often into the thousands, together with elevated bilirubin during the icteric phase.
• Coagulation studies (prothrombin time or international normalised ratio) should be checked to assess synthetic liver function and screen for evolving fulminant hepatic failure, particularly in more unwell or older patients.
• A relevant exposure history supports the diagnosis alongside serological confirmation. This includes travel to an endemic region, close contact with a confirmed case, or a recognised local outbreak source.

• There is no specific antiviral treatment for hepatitis A, and management is entirely supportive.
• Supportive care comprises rest, adequate hydration, avoidance of hepatotoxic substances including alcohol and, where possible, unnecessary hepatically metabolised medications, and antiemetics for symptomatic relief of nausea as needed.
• Close monitoring of liver function and coagulation studies is appropriate throughout the acute illness. International normalised ratio is the most sensitive early marker of evolving synthetic liver dysfunction.
• Any evidence of coagulopathy, encephalopathy or other features suggesting evolving fulminant hepatic failure needs urgent specialist liver assessment and consideration of transfer to a specialist liver unit.
• Post exposure prophylaxis for close contacts of a confirmed case is given within two weeks of exposure. It is hepatitis A vaccine for healthy individuals aged one to forty years.
• Human normal immunoglobulin (0.02 mL per kg intramuscularly) is used for those outside this age range, those who are immunocompromised, or those with chronic liver disease, where vaccine response may be less reliable.
• Pre exposure vaccination is recommended for travellers to endemic regions, men who have sex with men, people who inject drugs, those with chronic liver disease, and individuals in specific occupational risk groups.
• The hepatitis A vaccine is given as a two dose schedule at zero and six to twelve months for inactivated vaccine. It provides long term and highly effective protection.
• Strict hand hygiene and food and water safety precautions help limit onward transmission, particularly for travellers to endemic regions.
• Exclude infectious patients from food handling, healthcare and childcare occupations (generally until one week after onset of jaundice, according to local public health guidance).
• Notification to public health authorities is required given the potential for point source outbreaks and the importance of identifying and managing close contacts appropriately.