TORONTO -- Doctors across Canada and the United States are finding new clusters of a rare and unusual inflammatory condition in children that could be somehow linked to COVID-19.

In Toronto, the Hospital for Sick Children is the latest facility in Canada to report a cluster of cases of multisystem inflammatory syndrome in children (MIS-C), a condition that causes rashes in severe cases and can lead to heart damage if not treated, similar to Kawasaki disease.

“Over the last two to three weeks, we have seen about 20 children presenting with a combination of high fever and signs of inflammation, affecting one or more organs, quite similar to what has been reported internationally,” Dr. Jeremy Friedman, associate paediatrician-in-chief at the Hospital for Sick Children, told CTV News.

Friedman said the cluster began to emerge about three or four weeks after the COVID-19 outbreak began in Toronto.

Last month, doctors in Montreal reported more than a dozen cases. In an email, Dr. Fatima Kakkar, an infectious disease physician at Sainte-Justine Hospital in Montreal, said she’s been seeing another two or three cases each week since first reporting the cluster.

According to Kawasaki Disease Canada, an estimated 30 children out of 100,000 fall ill with the disease and as many as 80 per cent of cases involve children under the age of five.

However, Friedman said that in this latest cluster, some patients are as old as teenagers and average to be about nine years old.

He added that the children have shown a wide spectrum of symptoms, including rashes, swollen palms and vomiting, but each one of them presented to hospital with a high fever.

One of the 20 children needed treatment in the intensive care unit, while others were given immune modulating medications and improved.

“I have to say that the 20 children that we have seen have not been as sick or as severe as some of the reports that we've heard about,” he said.

The Ontario government has since listed the condition as a rare symptom of COVID-19 in children.

In British Columbia, Provincial Health Officer Dr. Bonnie Henry said on Monday the province is investigating “at least half a dozen” similar cases, though they still don’t know if the cases are connected to COVID-19.

“We don't have any known confirmed cases related to COVID-19 yet in the province, but that investigation is still ongoing,” Henry told reporters.

“It is quite rare still and there has been three, that I'm aware of, deaths in the United States of children. So it is something that we are watching very, very carefully.”

Dr. Stephen Freedman, a child health and wellness researcher at the University of Calgary who’s leading an international study of COVID-19 in children, said that MIS-C is not yet a reportable disease in Canada, so national numbers when it comes to the condition are not known.

He does believe, however, that it will be soon, meaning doctors could soon have a better understanding of how prevalent MIS-C is among children with and without a history of COVID-19.

The Canadian Paediatric Surveillance Program (CPSP) recently sent out an alert to Canadian doctors about the illness, stating that it has been found in children who have tested positive for COVID-19 and children who have tested negative, and can resemble toxic shock-like syndrome or Kawasaki disease.

In the U.S., at least 20 states and Washington, D.C. have reported similar cases. More than 100 cases have been recorded in New York alone, including three deaths.

What makes many of these cases puzzling is that the children often test negative for COVID-19, but later show antibodies to the virus.

“I think that's the million-dollar question,” Friedman said. “I would have to say that all 20 cases we've seen have all tested negative for COVID-19 on the nasal swab.”

“What has been found internationally -- certainly in Europe and now in the United States -- is that many of these children who are tested for antibodies will test positive, which suggests that they were infected, maybe weeks before they presented at SickKids.”

Friedman said doctors have taken blood samples from each of their patients and plan to test the samples for antibodies once there is a test that they deem reliable.

Doctors, meanwhile, stress that the condition is rare and treatable, but parents should watch for unusual fevers in their children that last for longer than a couple days.

"If it's associated with any kind of rashes or pink eye, or swollen lymph nodes or swollen hands or feet, then certainly they should reach out to their primary care provider,” said Dr. Camille Sabella, a pediatric infectious disease specialist at the Cleveland Clinic in Cleveland, Ohio.