Hepatitis is spreading "alarming" among children in the United States, with 11 cases reported so far in children aged 1 to 6, and dozens of other cases are being investigated in Europe.

The Centers for Disease Control and Prevention in the United States issued a health "warning" about 9 cases of unusual acute hepatitis in children in Alabama on Thursday.

NBC News reported that two cases were identified in North Carolina and dozens of other cases in Europe.

What should parents know?

Parents should be aware of the symptoms of hepatitis, which overlap with adenoviruses and hepatitis, such as diarrhea and nausea.

David Hill, spokesperson for the American Academy of Pediatrics, said: "Viruses usually take their course without the need for medical intervention, but sometimes hepatitis leads to hospitalization and may even require a liver transplant."

To distinguish between adenovirus symptoms and hepatitis symptoms, parents should monitor sick children and watch for severe abdominal pain, fever, dark urine, or pale stools.

Niboni Rajapaksi, a pediatric infectious diseases specialist, said that the most important symptoms to watch for are jaundice, meaning yellow discoloration of the skin or the whites of the eyes.

Esther Israel, head of the pediatric gastroenterology and nutrition unit at Mass General Hospital for Children, said: "At this time, practicing good hygiene habits, such as frequent hand washing or sanitizing, staying home when sick, and avoiding sick people are the best ways to prevent."

She added: "At this point, it is difficult to know how widespread this is, but we may see more if it is contagious. Parents should watch for signs of hepatitis and contact a healthcare professional if they are concerned."