The deaths of five children and what may be an unusual group of more than 100 cases of hepatitis in young children in the United States are under investigation by the Centers for Disease Control and Prevention, the agency said on Friday.
The CDC said it was investigating cases involving 109 children in 25 states and territories who had or have what the agency calls “hepatitis of unknown cause.”
dr. Jay Butler, deputy director for infectious diseases at the CDC, said most of the children made a full recovery. But more than 90 percent were hospitalized, 14 percent received a liver transplant and more than half had adenovirus infections, he said.
The CDC and foreign experts are investigating whether a type of adenovirus, a common virus that causes gut symptoms such as vomiting and diarrhea, could be a factor in these cases. But the agency has not identified a cause for the cases or a common link between all cases, and it warned against jumping to conclusions.
dr. Butler called it “an evolving situation” in a news conference on Friday. He later added, “It’s important to remember that severe childhood hepatitis is rare, even with the potential increase in cases we’re reporting today.”
Inflammation of the liver, usually caused by a virus, hepatitis carries a host of complicating factors, side effects and stigma.
Hepatitis and liver failure are uncommon events in young children, especially in otherwise healthy children, and so far the true number of hepatitis cases in the United States has been no more than the number commonly seen.
The agency did not provide details about the children who died or where those deaths occurred.
The UK is investigating a much larger number – more than 160 cases – of young children who have or have recently had hepatitis.
Hepatitis, a liver infection, usually occurs in adults and can be caused by viruses — which respond to drug treatment — or by alcoholism, by certain medications, or by autoimmune disorders. Symptoms include yellow skin and eyes, nausea, and abdominal pain.
dr. Butler also said there was no evidence to date that a Covid-19 infection or the Covid vaccine was linked to the US cases. The World Health Organization also said this week that the “vast majority” of children had not been vaccinated in the cases it assessed.
The alarm started two weeks ago when the CDC issued a warning, citing nine cases of hepatitis among young children in Alabama that started last fall this year. They all had evidence of an adenovirus infection. Their mean age was 2.
The problem for the CDC is determining whether the adenovirus is a cause or an innocent bystander, said Dr. Butler. Doctors don’t normally test children for adenovirus infections — it’s not a notifiable disease in the United States — making it difficult to untangle causes and effects. He urged doctors to consider testing for adenovirus if children were sick with certain symptoms.
It is not known how likely it is that nine randomly tested children would have had adenovirus infections. The virus is also seasonal, and fall and winter, when the kids in Alabama were sick, is adenovirus season.
Complicating the situation even more is that by the time the children were evaluated, the amount of virus, if any, was very low.
“We are working hard to determine the cause,” said Dr. Butler. Because hepatitis in children remains “a rare occurrence,” he said, the search is difficult.
Other possibilities include environmental exposure, including animal exposure or an immune response, with a response to an adenovirus “top of the list,” said Dr. Butler.
“We’re casting a wide net,” he said.