Hepatitis A

01Pathophysiology

Hepatitis A virus enters the body through ingestion of fecally contaminated food or water. After passing through the gastrointestinal mucosa, the virus reaches the liver via the portal circulation and preferentially infects hepatocytes. HAV itself is not directly cytopathic. Instead, the liver damage is caused by the host immune response, primarily CD8+ cytotoxic T lymphocytes that recognize and destroy infected hepatocytes. This immune-mediated injury is why the clinical illness and peak aminotransferase elevations occur several weeks after initial infection, coinciding with the appearance of the antibody response rather than with peak viral replication.

The destruction of hepatocytes leads to release of intracellular enzymes (ALT and AST) into the bloodstream, explaining the dramatic transaminase elevations seen in acute infection. Impaired bilirubin conjugation and excretion by damaged hepatocytes produces conjugated hyperbilirubinemia, which manifests clinically as jaundice, dark urine (bilirubinuria), and pale stools (decreased stercobilin). The nausea, anorexia, and malaise in the prodromal phase are attributed to circulating cytokines released during the immune response, particularly TNF-alpha and IL-1.

A critical concept for exam purposes is that HAV does not integrate into the host genome and does not establish a chronic carrier state. Unlike hepatitis B and C, HAV infection resolves completely in nearly all patients. The virus is shed in feces during the late incubation and early symptomatic period, meaning patients are most infectious before they even know they are sick. By the time jaundice appears and diagnosis is made, fecal shedding has already declined substantially. This timeline is frequently tested.

The incubation period averages 28 days (range 15 to 50 days). In rare cases (less than 1% of adults), a fulminant course with acute liver failure can occur, and this risk is significantly increased in patients who have pre-existing chronic liver disease, particularly chronic hepatitis C.

02Classification and Clinical Manifestation

HAV does not have formal clinical stages the way some diseases do, but the clinical course follows a well-defined progression that exam questions rely on. The table below outlines the phases of illness.

Additional clinical patterns worth knowing:

03Diagnostic Workup

The diagnosis of acute hepatitis A is straightforward compared to many other hepatic conditions. When a patient presents with acute jaundice, markedly elevated transaminases, and a compatible exposure history (travel, shellfish, daycare contact), the best initial test and the most accurate test are the same: anti-HAV IgM. This antibody becomes detectable at the onset of symptoms and persists for approximately 3 to 6 months. A positive anti-HAV IgM in the right clinical context is diagnostic; no liver biopsy or additional confirmatory testing is needed.

It is essential to understand the distinction between IgM and IgG because this is a favorite testing point. Anti-HAV IgM indicates acute or recent infection. Anti-HAV IgG, on the other hand, indicates prior exposure and immunity, either from a resolved past infection or from vaccination. If a patient has isolated anti-HAV IgG positivity with negative IgM, they are immune and do not have acute disease. If both IgM and IgG are positive, the patient is in the recovery phase of an acute infection (IgG begins to rise as IgM declines).

The aminotransferase pattern in HAV typically shows ALT greater than AST, with values frequently exceeding 1000 IU/L. This pattern of dramatic elevation distinguishes acute viral hepatitis from alcoholic hepatitis, where AST is classically greater than ALT in a 2:1 ratio and values rarely exceed 300 IU/L. If a vignette presents sky-high transaminases with ALT predominance, think acute viral hepatitis rather than alcoholic liver disease.

The one lab value you must always check in acute hepatitis is the INR/prothrombin time. A prolonged INR in the setting of acute hepatitis signals impaired hepatic synthetic function and raises concern for progression to fulminant hepatic failure. This is your trigger to escalate care and consider referral for liver transplant evaluation.

04Management and Treatment

There is no antiviral treatment for hepatitis A. Management of uncomplicated acute infection is entirely supportive. Patients should be advised to maintain adequate hydration, rest, and avoid alcohol and unnecessary medications that are hepatotoxic. Acetaminophen may be used cautiously at reduced doses for fever or pain, but should be avoided if transaminases are extremely elevated or if there is any concern for liver failure.

The most testable aspect of HAV management is post-exposure prophylaxis (PEP). When a close contact of a confirmed case is identified, the next best step depends on the patient's age and immune status. For healthy individuals aged 1 to 40 years, a single dose of the HAV vaccine given within 14 days of exposure is sufficient. For those younger than 12 months, older than 40, immunocompromised, or with chronic liver disease, immune globulin (IG) at 0.1 mL/kg intramuscularly is the preferred agent because the vaccine may not generate a sufficiently rapid immune response in these populations. In patients older than 12 months who receive IG, the vaccine should also be administered simultaneously (at a different injection site) to provide long-term immunity.

The HAV vaccine is an inactivated (killed) virus vaccine. The routine childhood schedule calls for the first dose at 12 months of age with a booster dose 6 to 18 months later. Adults traveling to endemic areas should receive the vaccine at least 2 weeks before departure. If travel is imminent (less than 2 weeks), both vaccine and IG should be given.

For the rare patient who develops fulminant hepatic failure (encephalopathy, INR > 1.5, rapidly worsening synthetic function), the management shifts to intensive care with immediate referral to a liver transplant center. Key interventions include correction of coagulopathy, glucose monitoring, management of cerebral edema, and lactulose for hepatic encephalopathy.

A contraindication worth noting: the HAV vaccine is not given to infants younger than 12 months because maternal antibodies may interfere with vaccine immunogenicity. In this age group, IG is the sole option for prophylaxis.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on hepatitis A questions is by confusing the serologic markers. When a vignette describes acute hepatitis and asks for the confirmatory test, the answer is anti-HAV IgM, not IgG. Selecting IgG is a trap because IgG indicates immunity, not active disease. Similarly, students sometimes confuse HAV with hepatitis E because both are transmitted by the fecal-oral route and both are self-limiting. The discriminator is the clinical context: if the patient is a pregnant woman with fulminant liver failure and fecal-oral exposure, think hepatitis E, not A. Hepatitis E carries a uniquely high mortality rate in pregnancy, and this association is tested repeatedly.

Another frequent trap involves post-exposure prophylaxis timing and patient selection. Students often default to giving immune globulin to everyone, but for a healthy adult between 1 and 40 years old, the vaccine alone is the correct answer within the 14-day window. IG is reserved for the very young, the elderly, the immunocompromised, and those with chronic liver disease.

Finally, remember that patients with HAV are most infectious before they become jaundiced, during the late incubation and prodromal phase when fecal viral shedding is at its peak. By the time the diagnosis is clinically apparent, the window of highest transmission has already passed. This concept is tested to assess whether you understand the natural history and can apply infection control principles correctly. The core competency being tested across all HAV questions is your ability to distinguish it from other causes of acute hepatitis using serologic markers, to identify who needs prophylaxis and what kind, and to recognize that this infection is self-limiting and does not lead to chronic liver disease.