Top 5 Takeaways

  1. Significant number of pediatric hepatitis cases: From October 1, 2021, to June 15, 2022, 296 pediatric patients in the U.S. were diagnosed with hepatitis of unknown etiology, with adenovirus detected in 45% of cases.
  2. Severe outcomes in some cases: Among the cases, 89.9% were hospitalized, 6.1% required a liver transplant, and 3.7% resulted in death.
  3. No common exposures identified: Preliminary analyses did not find any common exposures, such as travel or toxicants, that could explain the outbreak.
  4. Adenovirus as a potential factor: The detection of adenovirus in a significant portion of cases raises questions about its role, although it’s traditionally not a known cause of hepatitis in healthy children.
  5. Investigation continues: The CDC continues to collect data and encourages clinicians to report new cases and consider testing for adenovirus and SARS-CoV-2 antibodies, highlighting the need for further research to understand the etiology.

Original Article Author and Citation

Corresponding Author

Jordan Cates,

Suggested Citation

Cates J, Baker JM, Almendares O, et al. Interim Analysis of Acute Hepatitis of Unknown Etiology in Children Aged <10 Years — United States, October 2021–June 2022. MMWR Morb Mortal Wkly Rep 2022;71:852–858. DOI:


The CDC reported a total of 296 pediatric patients with hepatitis of unknown etiology in the U.S. between October 2021 and June 2022, with a significant number of cases testing positive for adenovirus. No common exposures were identified, and the outbreak’s cause remains under investigation.


Patients under investigation (PUIs) were defined as children aged <10 years with elevated liver enzymes and hepatitis onset after October 1, 2021. Data collection involved medical chart abstractions, interviews, and laboratory testing, including adenovirus PCR testing.


The involvement of adenovirus, especially adenovirus type 41, is notable, though it’s typically not associated with hepatitis in healthy children. The CDC continues to investigate the outbreak’s cause, including the role of adenovirus and potential previous SARS-CoV-2 infection.


The ongoing investigation highlights the need for continued surveillance, reporting, and research to understand the cause of these hepatitis cases. Clinicians are urged to report new cases and consider adenovirus and SARS-CoV-2 antibody testing.


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