hepatitis A

hepatitis A is an acute infectious disease of the liver caused by the Hepatitis A virus. It is one of several types of viral hepatitis, distinct from hepatitis B and hepatitis C. The illness is typically spread through the fecal–oral route, often via contaminated food or water, and is closely associated with inadequate sanitation and poor personal hygiene. Most infections in children are asymptomatic, while in adults, the disease can cause significant morbidity but usually resolves completely without chronic sequelae.

Signs and symptoms

The incubation period averages 28 days, after which symptomatic individuals may experience a prodrome of malaise, anorexia, nausea, and fever. This often progresses to clinical jaundice, with dark urine and pale stools, accompanied by hepatomegaly and right upper quadrant abdominal pain. A small percentage of patients may develop a relapsing form of the illness, and in rare instances, it can precipitate fulminant hepatitis, leading to acute liver failure. The severity of symptoms often increases with age, with infections in young children frequently going unrecognized.

Cause and transmission

The causative agent is the Hepatitis A virus, a picornavirus classified in the genus Hepatovirus. It is a non-enveloped, single-stranded RNA virus that is remarkably stable in the environment. Transmission occurs predominantly via the fecal–oral route. Common sources include ingestion of contaminated food, such as raw or undercooked shellfish from polluted waters, or produce irrigated with contaminated water. Outbreaks have been linked to food handlers in restaurants and to institutions like day care centers. Person-to-person spread is common in households and among men who have sex with men. The virus can also be transmitted through contaminated blood products, though this is rare.

Diagnosis

Diagnosis is confirmed by serological testing, specifically the detection of IgM antibodies to HAV in the blood serum, which appear during the acute phase of the illness. The presence of IgG antibodies indicates past infection or successful vaccination and confers lifelong immunity. Liver function tests typically reveal elevated levels of serum aminotransferase, particularly alanine transaminase and aspartate transaminase. The virus itself can be detected in stool samples by techniques like polymerase chain reaction, but this is not routinely used for clinical diagnosis.

Prevention

Effective prevention strategies include improved sanitation, access to safe water, and rigorous personal hygiene, especially handwashing. The most effective medical intervention is vaccination with the Hepatitis A vaccine, which is part of routine childhood immunization schedules in many countries, including recommendations by the World Health Organization and the Centers for Disease Control and Prevention. For unvaccinated individuals exposed to the virus, post-exposure prophylaxis with the vaccine or immune globulin can prevent or attenuate the disease. Travelers to endemic regions are strongly advised to receive the vaccine.

Treatment and prognosis

There is no specific antiviral therapy; management is entirely supportive care. This includes adequate hydration, nutritional support, and avoidance of substances like alcohol and certain medications that can further stress the liver, such as acetaminophen. Hospitalization may be required for severe nausea, vomiting, or signs of liver failure. The prognosis is generally excellent, with the vast majority of patients making a full recovery within two months. Chronic infection does not occur, and case fatality rates are very low, though they are higher in older adults and individuals with pre-existing chronic liver disease.

Epidemiology

Hepatitis A has a global distribution, with high endemicity in regions of Africa, Asia, and parts of South America where sanitation infrastructure is underdeveloped. In these areas, most children are infected asymptomatically, leading to widespread adult immunity. In developed nations like the United States and Western Europe, where endemicity is low, outbreaks can occur in communities with low vaccination coverage or among high-risk groups. Major outbreaks have been documented, including a 2016 epidemic linked to frozen strawberries in the United States and a 2017 outbreak among the homeless population in San Diego. The World Health Organization estimates millions of infections occur annually worldwide.