(HealthDay News) — The World Health Organization said it is investigating an outbreak of acute hepatitis among children that now involves 11 countries, including the United States.

Among the 169 reported cases, at least 1 child has died from this inflammation of the liver and 17 children needed liver transplants, the WHO said Saturday in a statement. “It is not yet clear if there has been an increase in hepatitis cases, or an increase in awareness of hepatitis cases that occur at the expected rate but go undetected,” the WHO said. “While adenovirus is a possible hypothesis, investigations are ongoing for the causative agent.” The symptoms “among identified cases [include] acute hepatitis with markedly elevated liver enzymes,” the statement added.

Among these recent infections, adenoviruses have been detected in at least 74 cases, but they typically do not cause severe hepatitis in healthy people. The common viruses that cause acute viral hepatitis, including hepatitis viruses A, B, C, D, and E, have not been detected in any of these cases, according to the WHO. While most of the children did not have a fever, many reported gastrointestinal symptoms such as abdominal pain, diarrhea, and vomiting “preceding presentation with severe acute hepatitis,” as well as increased levels of liver enzymes and jaundice.

Most of the 169 cases were reported in the United Kingdom, which had 114. Nine cases were reported by the Alabama Department of Health last week. Investigators are also aware of 13 cases in Spain, 12 in Israel, and smaller numbers in Belgium, Denmark, France, Ireland, Italy, the Netherlands, Norway, and Romania. The children are aged between 1 month and 16 years.

The WHO said the investigation needs to focus on “increased susceptibility amongst young children following a lower level of circulation of adenovirus during the COVID-19 pandemic, the potential emergence of a novel adenovirus, as well as SARS-CoV-2 coinfection.”

Late last week, the U.S. Centers for Disease Control and Prevention issued a health advisory about the acute cases of hepatitis with unknown cause. The CDC recommended providers consider adenovirus testing in children with hepatitis when the cause is unknown. Testing the blood in whole, rather than just blood plasma, may be more sensitive, the CDC advised.

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