Hepatitis A

What is hepatitis A?

Hepatitis A is a highly contagious liver infection caused by the hepatitis A virus (HAV).1 The hepatitis A virus replicates in the liver, transports through the bile, and is excreted into the feces via the biliary system.2

Hepatitis A can cause mild illness lasting a few weeks to a severe illness lasting several months.1

Range of Hepatitis A Symptoms From Mild (Lasting a Few Weeks), to Severe (Lasting Several Months)
Lasting a few weeks
Lasting several

Humans are the only natural host for the hepatitis A virus.2

What are the symptoms of hepatitis A?

The likelihood of symptomatic illness from the hepatitis A virus (HAV) is directly linked to age. Adults with HAV infection usually experience symptoms; however, hepatitis A in children under 6 years of age is largely asymptomatic. In fact, nearly 70% of children under 6 years of age with HAV infection show no symptoms.2,3

For those who experience symptoms, the onset is typically abrupt and includes:1,2,3

  • Jaundice
  • Fever
  • Fatigue
  • Loss of appetite
  • Nausea
  • Abdominal pain
  • Dark urine

How serious is hepatitis A?

Most people who get hepatitis A recover completely; however, in rare cases, hepatitis A can cause liver failure and death. This is more common in people older than 50 and in people with other liver diseases.1

How is hepatitis A transmitted?

The transmission of the hepatitis A virus infection occurs from person-to-person contact through the fecal-oral route or by consuming contaminated food or drink. In very rare instances, the transmission of HAV infection can occur through the use of contaminated blood and blood products.2

Can hepatitis A be transmitted if someone has no symptoms?

Yes. Most children under the age of 6 who have been infected display no symptoms of hepatitis A but could spread the virus. A person can also spread the virus up to 2 weeks before symptoms appear.1

How long do the symptoms of HAV infection last for those who display symptoms?

Usually, symptoms do not last longer than 2 months; however, 10% to 15% of people with HAV experience prolonged or relapsing symptoms for up to 6 months.2

What is the incubation period for hepatitis A?

The average incubation period for hepatitis A is approximately 28 days (range: 15–50 days).2

Can HAV survive outside the body? How can the hepatitis A virus be killed?

Depending upon environmental conditions, HAV can live outside the body for months. Heating food at temperatures >185° F (>85° C) for 1 minute or disinfecting surfaces with chlorine can inactivate HAV; however, the virus is still capable of being spread if food contamination occurs after cooking.1,2

Waterborne outbreaks of HAV in developed countries are rare; occurrences of this nature are generally attributed to sewage contamination and inadequately treated water.2,4

HAV can live for months on common objects.1

How is hepatitis A diagnosed?

A hepatitis A diagnosis is made through an evaluation of symptoms and a blood sample.1

How prevalent is hepatitis A?

In 2017, a total of 3,366 cases of hepatitis A were reported to the CDC from all 50 states and the District of Columbia. The overall incidence rate in 2017 was 1.0 reported cases per 100,000 population. After adjusting for under-ascertainment and under-reporting, an estimated 6,700 hepatitis A cases (95% bootstrap confidence intervals=4,700–7,400) occurred in 2017.5

What are some of the risk factors for hepatitis A infection?

Hepatitis A risk factors include2:

  • International travel (particularly with high-risk itineraries like travel to rural areas in high-risk countries)
  • Being a male who has sex with other men
  • Using illegal drugs
  • Having a clotting factor disorder
  • Having an occupational risk of infection

Does recovery from hepatitis A infection lead to lifelong immunity?

Yes, once a person has recovered from HAV infection, anti-HAV IgG antibodies remain in the person’s blood. This provides lifelong protection against HAV disease.2,3

How is hepatitis A treated?

People who have recently been exposed to the hepatitis A virus, and who have not previously received the hepatitis A vaccine, should be administered a single dose of single-antigen hepatitis A vaccine or immune globulin (IG) as soon as possible.6 For treating symptoms, doctors usually recommend rest, adequate nutrition, and fluids. They also recommend avoiding alcohol and using medication with care as the liver heals.1,7

CDC Disease Information

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CDC=Centers for Disease Control and Prevention; HAV=hepatitis A virus; IgG=immunoglobulin G.



  1. Centers for Disease Control and Prevention (CDC). Hepatitis A Questions and Answers for the Public. https://www.cdc.gov/hepatitis/hav/afaq.htm. Updated September 10, 2019. Accessed September 26, 2019.

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CDC Information

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Merck does not review or control the content at the site to which this link connects. Merck makes no representation with respect to the content of any non-Merck site.



  1. Centers for Disease Control and Prevention. Hepatitis A. In: Hamborsky J, Kroger A, Wolfe S, eds. Epidemiology and Prevention of Vaccine-Preventable Diseases. 13th ed. Washington, DC: Public Health Foundation; 2015:135–148. http://www.cdc.gov/vaccines/pubs/pinkbook/index.html. Accessed July 6, 2018.


  1. Centers for Disease Control and Prevention. Viral Hepatitis. http://www.cdc.gov/hepatitis/hav/. Updated June 13, 2019. Accessed September 26, 2019.


  1. Centers for Disease Control and Prevention. Prevention of hepatitis A through active or passive immunization: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2006;55(RR-7):1–23.


  1. Centers for Disease Control and Prevention. Viral hepatitis surveillance—United States, 2017. https://www.cdc.gov/hepatitis/statistics/2017surveillance/pdfs/2017HepSurveillanceRpt.pdf. Updated September 10, 2019. Accessed September 26, 2019.


  1. Centers for Disease Control and Prevention. Update: Prevention of Hepatitis A After Exposure to Hepatitis A Virus and in International Travelers. Updated Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2007;56(41): 1080–1084.


  1. Mayo Clinic. Hepatitis A Diagnosis & Treatment. https://www.mayoclinic.org/diseases-conditions/hepatitis-a/diagnosis-treatment/drc-20367055. Updated March 6, 2019. Accessed September 26, 2019.

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