Doctors remain mystified by the source of an outbreak of a severe liver disease in children.

Now, U.K. health officials believe a spike in hepatitis cases among children may be linked to COVID-19 lockdowns. Doctors in the U.K. believe children are getting the illness because of weakened immune systems due to lack of exposure to illnesses during lockdowns. 

Research is continuing, but experts believe the hepatitis spike is linked to the adenovirus, which is like the common cold.

"It has been detected in around 74 of those cases that have actually been tested for this," says Phillipa Easterbrook, a WHO senior scientist. "It is very unusual for an adenovirus to cause this type of severe symptoms."

NEARLY 200 CASES OF MYSTERY LIVER DISEASE IN CHILDREN: OFFICIALS

Hepatitis B

Hepatitis B (iStock)

Doctors say nearly 200 children in 12 countries have been diagnosed with acute hepatitis, which causes liver inflammation. Seventeen of those children have gotten liver transplants. At least one child has died. 

WHO: 1 CHILD HAS DIED IN MYSTERY LIVER DISEASE OUTBREAK

Illinois health officials say they are now investigating three cases of severe hepatitis in children in recent weeks. This follows a cluster of nine cases in Alabama and two more in North Carolina last month.

As more cases are found, the CDC issued a nationwide alert for doctors to watch for symptoms, asking medical professionals to keep a closer eye on children with cold and flu-like symptoms. Doctors caution parents not to be scared, but vigilant.

Blood sample for liver function test

It’s estimated 75% of people infected with hepatitis C, one of the most common forms of liver disease, are unaware that they’re infected. (iStock)

"The main symptoms to look out for with inflammation of the liver or hepatitis are severe abdominal pain, yellow eyes, yellow skin," says Dr. Karen Acker, a pediatrician at New York-Presbyterian Komansky Children’s Hospital and a professor at Weill Cornell Medicine.

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Doctors say they expect case numbers to rise and remind the public the best way to protect against illness is to wash hands.