Seven probable cases of severe acute hepatitis have been reported over a six-month period at one of Canadas major childrens hospitals, as an unexplained outbreak of severe cases is affecting healthy, young children around the world.

Hepatitis is an inflammation of the liver. Acute hepatitis is when the liver function is impaired for less than six months, while chronic hepatitis is when the inflammation lasts longer.

Ten cases of unexplained hepatitis were first reported in Scotland in early April. However, in a briefing on Tuesday, the World Health Organization (WHO) said there are now 348 probable cases of acute hepatitis in kids across five regions globally.

The Hospital for Sick Children in Toronto said on Monday the hospital has come across seven cases that met Public Health Ontarios case definition of acute hepatitis and cannot confirm if any of these cases were “caused by a novel clinical entity.

Shared Health also confirmed on Tuesday one pediatric case of severe acute hepatitis in recent weeks in Manitoba.

In a statement to CTV News, the Public Health Agency of Canada (PHAC) confirmed that there is an ongoing investigation into the rising hepatitis cases, both in Canada and internationally, but it currently remains unclear if the cases in Toronto are part of the unexplained global outbreak.

The cause of the cases of hepatitis among children remains unclear.

“Typically we think of viral causes like hepatitis A or hepatitis B or hepatitis C, but none of the typical viral links have been found in these particular cases,” CTV News medical specialist Dr. Marla Shapiro said Tuesday.

“So we dont know what the cause is. There has been some association worldwide with adenovirus, which is a fairly common virus. Some of these children have tested positive for COVID-19 as well, but we dont really think that this is a link to COVID.”

Current investigations suggest a link to an adenovirus, according to the WHO and ECDC. Adenoviruses make up a large family of viruses that can spread from person to person, causing a range of illnesses including colds, pinkeye and gastroenteritis.

Officials say there has been a recent rise in adenovirus infections, particularly in the U.K.

Close to half of the hepatitis cases, including those in the U.S., have been tied to an adenovirus, with lab tests indicating some children were infected with type 41, which is associated with gastroenteritis, causing diarrhea and vomiting. At least 19 cases also involved a COVID-19 co-infection.

Experts say that a lack of a cause is concerning because the severity of hepatitis is often determined according to its cause, as while some of the unexplained cases in kids have been mild, others have required liver transplants.

The WHO has reported that the outbreak has led to 17 liver transplants globally, and at least one death has been reported in the U.K.

Despite this, Dr. Dina Kulik, a Toronto-based pediatrician says parents should not panic.

“So we have seen over 200 cases of severe acute hepatitis around the world. That being said, there are millions and millions of children around the world. So while 200 plus cases are concerning, and definitely something to look into and be alert to, it isnt something we need to panic about at this point,” she told CTV News Channel on Tuesday.

Kulik did note that hepatitis symptoms can often mask themselves as that of the stomach flu or even COVID-19, with children experiencing fever, vomiting, diarrhea and stomach pain.

“But in particular, different from typical stomach flu kind of symptoms, kids will develop jaundice which is a yellow discoloration of the skin and yellow discoloration of the white of the eyes,” she said, adding that cautionary measures to prevent cases are hard to prescribe with the official cause still unknown.

The PHAC has not confirmed if there is an increase in the number of cases of acute hepatitis in Canada, but says they are “prepared to carefully and thoroughly investigate any cases reported that meet the national case definition.”

PHAC also recommends that parents should look out for symptoms that also include dark urine, loss of appetite, and light-coloured stools.