MINNEAPOLIS (WCCO) – Experts are investigating multiple theories as to why a mysterious case of severe hepatitis is affecting clusters of children across the world.

As of May 1, the World Health Organization was reporting 228 cases of hepatitis in children with no known cause. These cases are not a type of virus that children can be vaccinated against.

READ MORE: COVID In Minnesota: Total Positive Case Count Surpasses 1.5 Million

“Relatively few of them have tested positive for COVID-19 at the time of their diagnosis,” said Dr. Nipunie Rajapakse, from Mayo Clinic’s Children’s Center.

Researchers are, however, looking into if the cases are a delayed response to COVID-19, similar to MIS-C. Most of the children affected are under the age of five, who are not eligible for a COVID-19 vaccine.

A common link among the children is something called the adenovirus.

“These are relatively common viruses in the community and children commonly get infected with them,” Dr. Rajapakse said.

READ MORE: Record Number Of Baby Bison Born At Minneopa State Park

It causes symptoms like cough, runny nose, fever or diarrhea. Many but not all of the affected children had a type called adenovirus 41.

“Are kids just more vulnerable to this adenovirus infection because of the precautions we’ve been taking to avoid COVID-19,” Dr. Rajapakse asked. “And avoidance of infection over the last couple years, that’s another idea.”

Signs of liver failure include loss of appetite, dark urine, yellow around the eyes and skin, and fatigue.

Some of the children with these mysterious hepatitis cases are being hospitalized and requiring liver transplants.

As experts work to learn more, they emphasize the condition is still rare.

MORE NEWS: Sheriff: Motorist Killed In Wright Co. After Hitting Dump Truck Head-On

“I think anytime you’re worried about your child’s health for sure reach out to your health care provider,” said Dr. Rajapakse.

Kate Raddatz