An outbreak of at least 169 cases of acute hepatitis among children across 12 countries has led to at least one death and 17 liver transplants, according to the World Health Organization.
The WHO news release from April 23 followed an alert issued by the Centers for Disease Control and Prevention last week about a cluster of nine cases of severe hepatitis among kids in Alabama. (Two cases have also been reported in North Carolina and three in Illinois.) Hepatitis is a severe inflammation of the liver that can affect its function.
Investigators for WHO are working to determine the cause of the outbreak, which has been primarily in the United Kingdom. The common viruses that cause acute hepatitis have been ruled out. The U.K. has the most cases with 114, following by Spain (13), Israel (12) and the U.S. (9). WHO did not specify where the death occurred.
Related: CDC issues alert for severe hepatitis in kids: What parents need to know
The children affected range in age from one month to 16 years old. Symptoms in the cases reported include jaundice, abdominal pain, diarrhea and vomiting, as well as increased levels of liver enzymes.
WHO and CDC are investigating a possible connection between the hepatitis cases and a strain of adenovirus known as adenovirus 41, a common virus that often causes cold-like symptoms like a sore throat, stomach pain or diarrhea. Adenovirus has been detected in at least 74 of the 169 cases reported, according to WHO.
"While adenovirus is currently one hypothesis as the underlying cause, it does not fully explain the severity of the clinical picture," the WHO wrote in its news release. "Infection with adenovirus type 41, the implicated adenovirus type, has not previously been linked to such a clinical presentation."
A Monday briefing from the U.K. Health Security Agency explained that 40 of 53 of the country's cases that had been tested for adenovirus were positive. During the pandemic, cases of adenovirus fell in the U.K., but they're now higher than pre-pandemic levels. That said, it's not yet clear how an infection with an adenovirus may lead to liver inflammation. U.K. health officials are investigating a few possible explanations, including prior COVID-19 or other infection, an undiscovered co-infection or toxin, a new strain of adenovirus, or "increased susceptibility" due to reduced exposure to other people during the pandemic.
According to WHO, the "vast majority" of affected children did not receive the COVID-19 vaccine, so the WHO does not believe it has anything to do with side effects from the vaccine.