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The infection is fecal-oral. The incubation period is about 2 to 6 weeks. An infected person can be contagious from 2 to 5 weeks before the onset of jaundice, until the disappearance of clinical symptoms. Acute hepatitis A can occur in small epidemics.

The disease never becomes chronic and its evolution depends on the age at which the infection occurs. In children, the disease is usually subclinical, while in people over 45 years of age, there is a mortality of more than 2% (partly due to acute liver failure).

Intake of estrogens (via oral contraception) may lead to cholestasis after the first phase of severe hepatitis. In a minority of adults the disease may be biphasic. Rarely acute hepatitis A provokes chronic autoimmune hepatitis. The diagnosis is made by an increase in bilirubin, a marked increase in transaminases and when the anti-hepatitis A IgM (class M immunoglobulin) becomes positive. Hepatitis A can be prevented by a vaccine. This is recommended when travelling to endemic areas. The first administration should preferably be received fourteen days before departure.

Acute hepatitis A does not require antiviral therapy. Urgent vaccination of the partner would make the course of the disease milder if there had been an infection.

Although this illness has decreased in developed countries due to extensive immunization, numerous developing and under-developed countries are struggling with this virus. HAV infection can be spread by oral-fecal contact, and there are frequent epidemics through nutrition. Improvements in socioeconomic and sanitary circumstances have caused a shift in the disease's prevalence worldwide. Younger children are usually asymptomatic, but as they become older, the infection symptoms begin to appear. Symptoms range from slight inflammation and jaundice to acute liver failure in older individuals. While an acute infection may be self-limiting, unrecognized persistent infections, and the misapplication of therapeutic methods based on clinical guidelines are linked to a higher incidence of cirrhosis, hepatocellular carcinoma, and mortality. Fortunately, most patients recover within two months of infection, though 10–15% of patients will relapse within the first six months. A virus seldom leads to persistent infection or liver damage. The mainstay of therapy is based on supportive care. All children from 12–23 months, as well as some susceptible populations, should receive routine vaccinations, according to the Centers for Disease Control and Prevention and the American Academy of Pediatrics. Laboratory diagnosis of HAV is based on antigen detection, checking liver enzyme levels, and antibody screening. Furthermore, polymerase chain reaction (PCR) technology has identified HAV in suspected nutrition sources; therefore, this technique is used for preventative measures and food-related laws. 

HAV infection is highly contagious, and it is a leading cause of acute hepatitis. In people with chronic liver disorders, acute HAV infection can induce liver failure. HAV seroprevalence is also relatively low in high-income provinces. Socioeconomic factors, access to clean water, and proper sanitation are all strongly linked to epidemiology. HAV usually causes short-term, self-limiting illnesses that go away without any long-term effects in 4–7 weeks. Dissimilar to HBV and HCV, HAV seems not to cause persistent liver damage. However, particularly in the elderly, severe fulminant hepatitis with possibly fatal liver failure may ensue. The associated risk factors that cause case-to-case variation in the degree of liver disease and recurrence remain unclear. Furthermore, contact with the feces of infected patients with HAV can result in the transmission of the virus, implying that the virus can be spread via oral-fecal transmission. It is widespread, although it is more common in less-developed areas with inadequate sanitary and hygienic conditions. Transfusion transmission of HAV is exceedingly rare due to the short persistence of viremia throughout acute HAV infection (approx. 10–50 days). However, donors should be reminded that if they are identified with blood-borne diseases after donating blood, they must inform the blood center. If a transfused individual shows hepatitis A symptoms with no record of traveling or oral-fecal disease, doctors should evaluate the potential of transfusion-transmitted hepatitis A. 

In collaboration with state and local health departments, CDC launched a large-scale, multidisciplinary response in 2017 to control the ongoing outbreaks associated with person-to-person transmission. To provide hepatitis A vaccination to disproportionately affected populations most affected by the outbreaks, health departments developed and implemented nontraditional vaccination and staffing strategies. These included holding satellite vaccination clinics (e.g., at correctional facilities, substance use treatment facilities, syringe services programs, and homeless shelters) and broadening the scope of health care professionals approved to administer vaccines. To overcome barriers to vaccination, including mistrust, stigma, and vaccine hesitancy, health departments partnered with organizations that have long-standing, trusted relationships with persons at risk for HAV infection. In September 2022, as a result of these intensive and innovative efforts, 24 states have officially declared their outbreaks over, and the remaining 13 states report decreased case counts from the peaks of their outbreaks.

The findings in this report are subject to at least five limitations. First, risk factor data were self-reported and subject to recall and social desirability biases. Second, hepatitis A surveillance in the United States is passive; thus, case counts might underestimate the actual number of cases. Third, a substantial proportion of data was missing; caution should be exercised when interpreting results with high rates of missing data. Fourth, ethnicity was not systematically ascertained and could not be included. Finally, states did not use an identical hepatitis A–related death case classification, which might have resulted in differential classification of deaths as being hepatitis A–related.

Hepatitis A epidemiology in the United States has shifted as a result of the ongoing outbreaks associated with person-to-person transmission. Cases occurred almost exclusively among adults, and HAV transmission was driven primarily by close contact among persons who use illicit drugs and persons experiencing homelessness. Improving services for these populations, including access to substance use treatment and sanitation, are important considerations in mitigating HAV transmission. Many adults at increased risk for HAV infection remain vulnerable to infection, despite long-standing vaccination recommendations. Given the high hospitalization rate during these outbreaks and the high level of susceptibility to HAV infection among adults in the United States, efforts are needed to improve awareness of and adherence to ACIP hepatitis A vaccination recommendations. Increased hepatitis A vaccination coverage, through implementation of nontraditional vaccination strategies to reach disproportionately affected populations, along with improved universal and catch-up childhood vaccination, will be necessary to respond to the current hepatitis A outbreaks and prevent similar outbreaks in the future. Lessons learned during these outbreaks have been reinforced by experiences during the COVID-19 pandemic and other vaccine-preventable disease outbreaks. Disproportionately affected populations often experience stigma, mistrust, and societal barriers that limit adequate access to the health care system. Continued improvements in vaccination infrastructure, immunization information systems, and education and outreach are critically needed to build vaccine confidence and improve vaccine delivery in nontraditional settings.

Risk areas for travellers

Over the last decades, a substantial decrease in incidence of hepatitis A infection has been observed worldwide due to better food and water hygiene, improved sanitation, increasing socio-economic standards and (in few countries) the implementation of hepatitis A vaccine in the childhood vaccination programmes. Therefore, many countries are evolving from high and intermediate endemicity towards intermediate and low endemicity respectively.

Regions with high endemicity are sub-Saharan Africa and parts of South Asia (Afghanistan, Bangladesh, Bhutan, India, Nepal, Pakistan). Hepatitis A is typically acquired during childhood, providing immunity for nearly all adults. Considering most children experience an asymptomatic disease course, outbreaks are rather exceptional.

Intermediate endemic areas are Latin America, North Africa, the Middle East and multiple countries in Asia. The infection is less frequently acquired during childhood, leaving more adults susceptible to hepatitis A. Hence, outbreaks are more common.

Western Europe, Canada, USA, Australia, New Zealand and some high income countries in Asia (Japan, South Korea, Brunei, Singapore) have a low to very low endemicity. The risk of getting infected with hepatitis A virus in these areas is thus low.

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