Hepatitis A is a liver disease common in many parts of the world and caused by hepatitis A virus (HAV), a picornavirus that causes acute inflammation of the liver. It is not related to the common viruses that cause hepatitis B or C.
Ask the Experts: Hepatitis A: Disease Issues
Illness caused by HAV infection cannot be distinguished from other types of acute viral hepatitis, but it typically has an abrupt onset that can include fever, malaise, anorexia, nausea, abdominal discomfort, dark urine, and jaundice. The likelihood of having symptoms with HAV infection is related to age. In children younger than age 6 years, 70% of infections are asymptomatic. When illness does occur in young children, it is typically not accompanied by jaundice. In older children and adults, infection typically is symptomatic, with jaundice occurring in more than 70% of patients.
Hepatitis A signs and symptoms usually resolve in 2-3 months, although 10% to 15% of symptomatic people have prolonged illness (usually referred to as relapsing hepatitis A) lasting up to 6 months and should be considered infectious during that time.
Person-to-person spread through the fecal-oral route is the primary means of HAV transmission. Peak infectivity in infected people occurs during the two-week period before the onset of jaundice when the concentration of virus in the stool is highest and most people are no longer infectious one week after jaundice onset. Before routine vaccination of children was recommended, children were a key source of infection because most infected children had no symptoms and could shed virus in stool for weeks or months. Transmission currently occurs primarily among susceptible adults.
Common-source outbreaks and sporadic cases can occur from exposure to fecally-contaminated food or water. Uncooked HAV-contaminated foods have been recognized as a source of outbreaks. Cooked foods also can transmit HAV if the temperature during food preparation is inadequate to kill the virus or if food is contaminated after cooking, as occurs in outbreaks associated with infected food handlers. Transmission of the virus from infected food handlers to food service establishment patrons is rare, accounting for 0.2% of the nearly 23,000 outbreak-associated cases of hepatitis A investigated by state health departments during 2016-2019. In 2020, there were 9,952 cases reported to public health, although CDC estimates that the actual number of cases was closer to 19,900. This represents a 47% decrease from 2019.
Until 2017, US incidence rates of hepatitis A were driven by occasional outbreaks, often linked to viral contamination of imported food. Since 2017, communitywide outbreaks have occurred more frequently, predominantly among people who are connected by specific risk factors, such as drug use or homelessness, and their close contacts.
HAV can produce either asymptomatic or symptomatic infection in humans after an average incubation period of 28 days (range: 15–50 days).
In infected people, HAV replicates in the liver, is excreted in bile, and is shed in stool. Peak infectivity occurs during the 2-week period before onset of jaundice or elevation of liver enzymes, when concentration of virus in stool is highest. Concentration of virus in stool declines after jaundice appears, with most people no longer infectious about a week after jaundice appears. Children can shed HAV for longer periods than adults, up to 10 weeks or longer after onset of clinical illness.
The incidence of hepatitis A in the US increased more than 10-fold from 2015 to 2019, with over 18,800 cases reported to CDC in 2019. The number of reported cases declined by 47% to 9,952 in 2020. This number is an underestimate of the actual number of infections: CDC estimates that about 19,900 cases actually occurred in 2020.
Between 2012 and 2015 the number of reported hepatitis A infections ranged from approximately 1200 to 1800 cases every year. Beginning in 2016, large foodborne outbreaks led to an increase in the number of cases and sustained, large person-to-person outbreaks began, primarily driven by infections among unvaccinated people who use drugs and people experiencing homelessness and their contacts. Since then, persistent person-to-person outbreaks have led to substantial increases in hepatitis A infection, with 37 states reporting almost 45,000 cases over the 7 years between the beginning of the outbreaks in 2016 and June 2023. The rate of new cases has declined substantially since the peak in 2019. More information regarding ongoing multistate outbreaks can be found here: www.cdc.gov/hepatitis/outbreaks/2017March-HepatitisA.htm.
Yes. Death as a result of fulminant hepatic failure is rare, however, older age (over 40 years) and preexisting chronic liver disease increases the risk of severe disease and death from hepatitis A. The person-to-person U.S. multistate outbreaks that began in 2016 have disproportionately affected adults with chronic liver disease and other health problems related to drug use and unstable housing. From 2016 through June 2023, CDC received reports of nearly 45,000 cases of acute HAV infection. Of these, approximately 61% have been hospitalized and nearly 1% (more than 420 people) have died.
People who are at increased risk for acquiring HAV infection include the following:
- Travelers to countries that have high or intermediate endemicity of HAV infection
- Men who have sex with men (MSM)
- Users of injection and non-injection drugs (in other words, all who use illegal drugs)
- People with occupational risk of exposure (those who work with HAV-infected non-human primates or researchers handling hepatitis A virus)
- People who anticipate close contact with an international adoptee coming from a country with high or intermediate endemicity of HAV infection
- People living with HIV infection
- People experiencing homelessness, including temporary shelters and other unstable living arrangements
- People living in group settings for those with developmental disabilities and other settings where hygiene is difficult to maintain
- People who are incarcerated
Historically, HAV infection was highly endemic in institutions for people with developmental disabilities as a result of poor hand hygiene, close living conditions and diaper use. As fewer children have been institutionalized and as conditions in institutions have improved, the incidence and prevalence of HAV infection have decreased, although outbreaks can occur in these settings. All children with developmental disabilities should receive HepA vaccine according to U.S. routine vaccine recommendations, including catch up vaccination of all children through age 18 years.
As a strategy to further reduce the risk of hepatitis A outbreaks and reach adults in settings with a high proportion of people with risk factors for HAV infection, the current ACIP recommendations suggest considering HepA vaccination of residents and staff in facilities where hygiene is difficult to maintain, such as group homes for people with developmental disabilities and homeless shelters.
No. People with chronic liver disease are not at increased risk for acquiring HAV infection. However, they are at an increased risk for life-threatening, fulminant (severe and sudden) hepatitis if they become infected with hepatitis A. People considered to have chronic liver disease include those with hepatitis B or C infection, cirrhosis, fatty liver disease, alcoholic liver disease, and autoimmune hepatitis.
Hepatitis A cannot be differentiated from other types of viral hepatitis on the basis of clinical or epidemiological features alone. Appropriate blood tests must be used.
- Anti-HAV: Total antibody to HAV. This diagnostic test detects total antibody of both IgG and IgM subclasses of HAV. If positive, it indicates either acute or resolved infection.
- IgG anti-HAV: IgG antibody is a subclass of anti-HAV. It appears early in the course of infection, remains detectable for the person’s lifetime and provides lifelong protection against disease. Its presence indicates immunity through either HAV infection or HepA vaccination.
- IgM anti-HAV: IgM antibody is a subclass of anti-HAV. Its presence indicates a recent infection with HAV (6 months or less). It is used to diagnose acute (recently acquired) hepatitis A. Because of the risk of false positive IgM anti-HAV results, people should only be tested for IgM anti-HAV if they are symptomatic and suspected of having acute hepatitis A illness.
- HAV RNA tests also may be used to diagnose acute infection through the direct detection of viral RNA in serum or stool.
Total anti-HAV, which appears early in the course of infection, remains detectable for the person’s lifetime and indicates lifelong protection against the infection/disease. To confirm a diagnosis of acute HAV infection, serologic testing for IgM anti-HAV is required. In the majority of persons, serum IgM anti-HAV becomes detectable 5 to 10 days before onset of symptoms and lasts about 6 months. However, there have been reports of persons who test positive for IgM anti-HAV for up to a year or more following infection. An educational program on the interpretation of hepatitis A serology is available on the CDC website at www.cdc.gov/hepatitis/resources/professionals/training/serology/training.htm.
Yes. On rare occasions, HAV infection has been transmitted by transfusion of blood or blood products collected from donors during the viremic phase of their infection (i.e., when HAV is in the donor’s blood). Since 2002, tests to detect the presence of hepatitis A virus RNA in donated plasma have drastically reduced the risk of hepatitis A transmission from products derived from blood plasma.
In experimentally infected nonhuman primates, HAV has been detected in saliva during the incubation period; however, transmission by human saliva has not been reported.
Hospital-acquired HAV infection is rare. In the past, outbreaks were observed in neonatal intensive care units when infants acquired infection from HAV-infected transfused blood and subsequently transmitted HAV to other infants and staff. Outbreaks of hepatitis A caused by transmission from adult patients to healthcare personnel (HCP) are typically associated with fecal incontinence and inadequate hand hygiene, although the majority of hospitalized patients who have hepatitis A are admitted after onset of jaundice, when they are beyond the point of peak infectivity. Transmission in healthcare settings also has resulted from breakdowns in standard infection control practices and transmission from one healthcare provider to another.
Depending on conditions, HAV can be stable in the environment for months; freezing does not inactivate (i.e., render non-infectious) HAV. HAV is inactivated by heating foods to temperatures greater than 185°F (85°C) for 1 minute. In addition, HAV on surfaces is inactivated by disinfecting surfaces with a 1:100 dilution of sodium hypochlorite (i.e., household bleach) in tap water.
Adequately chlorinating water through water treatment processes and dilution in public water systems kills HAV. Spas and swimming pools that are adequately treated are not likely to pose a risk for HAV outbreaks.
No, there is no chronic (long-term) infection. Even the small proportion of people who develop relapsing HAV recover after about 6 months. Once you have had HAV infection and recovered, you cannot get it again.