Children with Hepatitis of Unknown Cause

CDC is currently working with health departments across the country to identify children with hepatitis of unknown cause. Investigators are examining a possible relationship to adenovirus type 41 infection.

In October 2021, five pediatric patients with hepatitis (inflammation of the liver) of unknown cause were identified in children at a hospital in Alabama. The children had significant liver illness, including some with liver failure, with no known cause. The five children tested negative for hepatitis A, hepatitis B, and hepatitis C viruses and tested positive for adenovirus, a common virus that typically causes cold- or flu-like illness, or stomach or intestine problems. An additional review of hospital records later identified four additional patients, all of whom had hepatitis and adenovirus infection.

All of the children were previously healthy and ranged in age from one to six years old at the time of hospitalization. The children were from different parts of the state. No known contact or common exposures were found among the children. None of the children had significant underlying medical conditions. The children are now all recovering.

Other patients with a similar illness are being investigated in other states.

CDC is also aware of an increase in pediatric patients with hepatitis of unknown cause in children recently reported in other countries, and CDC is working with public health officials around the world to understand what they are learning. Adenovirus has been detected in some of these patients throughout the United Kingdom and Europe, but not among all of them. Investigators are considering other possible causes and identifying other possible contributing factors.

Information for Specific Groups

What We Know

Laboratory tests identified that some of the children had adenovirus type 41, which is more likely to cause severe stomach illness in children.

Although there have been previous reports of hepatitis in children with suppressed immune systems who were infected with adenovirus, adenovirus type 41 is not a common cause of hepatitis in otherwise healthy children.

Other common causes of viral hepatitis, such as infection with hepatitis A, B, C, D, and E viruses were considered, but evidence for these infections were not found in any of the patients. Some other causes have been ruled out for the children in Alabama, including:

What We Don’t Know


At this time, the cause of the reported illnesses in these children is still unknown. While adenovirus has been detected in some children, we do not know if it is the cause of the illness.

We do not know and are investigating what role other factors play in this illness, such exposure to toxins or other infections that the children might have.

Prevalence (Number of Cases)

It is not yet clear whether there has been an increase in the number of cases of hepatitis in children, or improvements in detecting cases. It is not unusual for the cause of some hepatitis cases in children to remain unknown.

What CDC Is Doing


CDC is working with state and local health departments to see if there are additional U.S. pediatric patients with hepatitis, and what may be causing these illnesses. At this time, we believe adenovirus could be the cause of some of these reported illnesses, but investigators are still learning more – including ruling out other possible causes and identifying other possible contributing factors.

While rare, children may still get hepatitis, and we don’t always know the cause. To learn more about the potential causes of hepatitis in this investigation, investigators are working with state and local health departments to examine the medical records of children who had hepatitis in the past.

During this investigation, it may seem like there is a growing number of children with hepatitis, but this might not be the full picture. These may not be new cases of hepatitis, and they may not be linked to this current investigation.

CDC is also examining national data sources to look at trends in hepatitis in children (including disease requiring liver transplants), as well as any trends in adenovirus infection over several years, including before the COVID-19 pandemic.

CDC and state public health officials will continue to work in close collaboration with healthcare providers to identify and detect unusual patterns or clusters of hepatitis in children. As soon as they find clues, they will quickly share guidelines to prevent further disease.


CDC is asking healthcare providers to consider testing for adenovirus in pediatric patients with hepatitis of unknown origin, and to report any possible cases of hepatitis to their local or state public health authorities.

CDC is working closely with laboratories around the country to determine the best testing practices. CDC will share additional information as it becomes available. We are making recommendations for healthcare providers and laboratories about how to submit specimens for testing.

CDC is also engaging public health partner organizations to share information and make sure we are prepared to diagnose and treat additional cases. CDC will work with these partners to quickly disseminate a list of laboratories able to do adenovirus testing or typing.

Sharing Information

  • CDC has sent out a HAN (Health Alert Network) notification to healthcare providers and public health partners to help clinicians and state health departments learn more, including how to report any other potential cases they have identified. Additional HAN notifications are planned when there are clinical or laboratory updates.

What Parents Can Do

Hearing about severe liver disease in children can be concerning. If you have any questions about your child’s health, call your child’s healthcare provider. Other things you can do are:

  • Be aware of the symptoms of liver inflammation, which include:
    • fever
    • fatigue
    • loss of appetite
    • nausea
    • vomiting
    • abdominal pain
    • dark urine
    • light-colored stools (poop)
    • joint pain
    • jaundice (yellowing of the skin)
  • Keep children up to date on all their vaccinations.
  • Help your child take everyday actions to help prevent disease, like:
    • washing hands often,
    • avoiding people who are sick,
    • covering coughs and sneezes, and
    • teaching them to avoid touching the eyes, nose, or mouth.

Learn more about adenovirus.

How CDC Investigates New Clusters of Illness

Investigating the occurrence of more than the expected number of cases of an illness is a multistep process focused on answering three questions:

  • “What is the problem?”
  • “What is the cause?”
  • “What can we do about it?”

What is the problem?

To identify the problem, CDC creates a “case definition.” A case definition provides a common understanding of who has the illness and helps investigators as they collect data on those cases. The data collected helps scientists understand the size, timing, severity, and possible cause of the illness. Investigators keep track of the cases over time.

What is the cause?

The next step is to develop and assess theories about how or what might be happening to cause people to get sick around the same time. Developing theories about the cause of the illness is an ongoing process. Investigators use interviews, questionnaires, and other tools to help narrow down how and where people got sick. Theories about the cause of an illness are continually changed or disproved as more information is gathered.

What can we do about it?

As investigators identify the likely cause of the illness, they implement disease control and prevention activities to prevent the spread of the disease. Scientists continue to count the number of new cases and monitor the situation to determine if prevention measures are working and disease spread is being controlled.

Public health officials choose measures to control the spread of the illness based on the information available to them. Measures can change as the investigation goes on.

Page last reviewed: May 6, 2022