2022-05-20 On cases of unexplained acute hepatitis in children

The Japanese government has begun to identify the number of cases of acute hepatitis in children and publishes the results of its investigation in the following article.

For the moment, this hepatitis has not

About cases of unexplained acute hepatitis in children (May 20, 2022)

All countries in the world continue to report cases of acute hepatitis of unknown origin in children.

In order to identify the causes of this acute hepatitis, the World Health Organization (WHO) has established a provisional case definition and asks countries to report cases that meet this definition.

The Ministry of Health, Labor and Social Affairs sent in a circular on April 20, 2022, a vigilance alert and asked local governments to provide information on this point. He also sent a circular on April 27 on the follow-up of infected cases that meet these criteria and on active epidemiological investigations.

The cumulative number of cases reported between October 1, 2021 and May 19, 2022 at 10 a.m. that fall under the interim case definition (※) is published in the appendix. We will continue to compile and publish the status of case reports on a regular basis.

The Ministry of Health, Labor and Welfare will continue to monitor the infectious situation in other countries and collect information, in cooperation with their governments, WHO and experts.

We ask the press and each media to pay attention to respect for privacy and not to publish information leading to the identification of the persons concerned or their families, etc.


※ The provisional case definition is as follows. “Regarding the Occurrence of Unexplained Hepatitis in Children in the United States and Europe (Call for Cooperation) Circular of April 27, 2022, Office of Health, Ministry of Health, Labor and Social Affairs.

Hospitalized cases with unexplained hepatitis diagnosed on or after October 1, 2021, which can be classified as follows.

  • 1. Confirmed cases: none at this time.
  • 2. Potential cases: children 16 years of age or younger with acute hepatitis with an aspartate transaminase (AST) or alanine transaminase (ALT) > 500 IU/L, and for whom hepatitis virus involvement has been ruled out A to E.
  • 3. Epidemiologically relevant cases: people of any age with acute hepatitis who are contacts of potential cases.

Appendix: 小児の原因不明の急性肝炎について(令和4年5月20日報道発表)

Information (summaries of the appendix)

The government records a total of 24 cases between October 2021 and May 19, 2022. All are in the category of “potential cases”. Among them,

  • 2 tested positive for COVID-19
  • 2 tested positive for adenovirus. It should be noted that
    • The two cases of adenovirus are not the same type as those found in Britain.
    • 7 other cases managed in the regional health research centers await the results of further examinations.

As the study is done retroactively, some of these cases have already been discharged from the hospital and are feeling better. Therefore, all these cases do not necessarily date from April, and are not related to this recent epidemic.

On acute hepatitis

Acute hepatitis is diagnosed when patients have no symptoms or loss of appetite, general malaise, nausea/vomiting, pain in the right hypochondrium, dark urine, diarrhea, etc. and for which there is jaundice.

In the Japan Liver Transplantation Society liver transplant case registration report, acute liver failure is classified into HBV, drug-induced hepatitis, autoimmune hepatitis, viral hepatitis (non-HBV), hepatitis of unknown cause, etc

There were 41 liver transplants in pediatric care between 2018 and 2020. These aimed to treat

  • 2 viral hepatitis (non HBV),
  • 36 hepatitis of unknown cause,
  • 1 neonatal hemochromatosis,
  • 2 hepatitis of another type.

The cause of acute hepatitis varies by virus. The virus can be transmitted by mouth, by blood, during mother-child transmission, sexually, etc.

For all these types of hepatitis, treatment of the symptoms only is carried out. However, in the case of fulminant hepatitis, one may need to perform special treatment, such as plasmapheresis or adjuvant treatment with an artificial liver and liver transplantation.

Source: 小児の原因不明の急性肝炎について(令和4年5月20日) (mhlw.go.jp)

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