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Canadian doctors are looking into whether a rare and potentially severe inflammatory syndrome found recently in some Montreal children could have been triggered by the novel coronavirus.

Chief Public Health Officer Theresa Tam said Wednesday that investigations of the mystery illness are under way in Ontario and Quebec, while the Canadian Paediatric Society is preparing to send a bulletin to children’s physicians across the country asking them to be on the lookout for youngsters with the overlapping symptoms of Kawasaki disease and toxic-shock syndrome.

Kawasaki disease is an acute inflammation of the blood vessels that is usually accompanied by a prolonged fever, pink eye, swollen neck glands and swelling and redness on the palms and soles of the feet.

It is not at all clear that the Montreal cases are linked to the coronavirus, but doctors in COVID-19 hot spots in Europe and the United States have reported treating children with a similar constellation of symptoms, some of whom tested positive for the novel virus.

“The pediatric networks are looking at this and there have been cases identified,” Dr. Tam said, “[but] they haven’t been verified to be linked to COVID-19 specifically.”

The possibility, however slight, that the coronavirus could cause serious complications in a tiny number of children would be a departure from what is known about the pathogen that has shut down much of the world. The vast majority of national and international evidence shows that coronavirus-infected children usually experience mild symptoms and recover swiftly.

The most recent Public Health Agency of Canada (PHAC) figures say that people under the age of 19 make up 5 per cent of COVID-19 cases and just 1 per cent of those admitted to hospital. No Canadian children are known to have died of COVID-19, according to PHAC.

The cases at the centre of the investigation turned up at Montreal’s Sainte-Justine Hospital over the past few weeks, according to Marie-Paule Morin, a pediatric rheumatologist at the hospital.

Dr. Morin said Sainte-Justine has seen a “slight increase,” in the number of children with the symptoms of Kawasaki disease. The precise cause of Kawasaki disease is not known, but it is thought to be triggered by viral or bacterial infections.

Approximately 20 children, most under the age of 5, have been treated at Sainte-Justine for Kawasaki-like symptoms since the end of March, Dr. Morin said. Only one required treatment in the intensive-care unit and none died.

All the children tested negative for active COVID-19 infections. Blood tests are now under way to see whether any developed antibodies that would indicate their immune systems had fought off the coronavirus in the past.

The presence of antibodies would not prove the coronavirus is to blame; another type of infection could still be the culprit.

“It’s tricky to make the correlation," Dr. Morin said. “What we know is it seems like it’s happening once the coronavirus has probably been eliminated from the system, but the immune system got kind of over-reactive. That’s one hypothesis.”

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Sainte-Justine is giving its recent Kawasaki-like cases a second look because of new information that is emerging from other places that, like Montreal, have been hit hard by the coronavirus. The city is the epicentre of Canada’s outbreak.

New York City’s health department issued a bulletin Monday night describing 15 cases of a “pediatric multi-system inflammatory syndrome,” in children, five of whom had to be put on ventilators. None died.

Four tested positive for active COVID-19 infections through nasal-swab testing. Blood testing found that six of the 11 who tested negative had developed antibodies to the coronavirus.

Pediatricians in Italy, France, Spain and Britain have reported dozens of cases of the baffling syndrome, which has sometimes included symptoms of shock, such as dangerously low blood pressure. Children have also suffered vomiting, diarrhea and rashes.

Some have tested positive for the coronavirus and others haven’t, which is one reason it’s difficult to tease out the cause of the syndrome.

“I think what you’re seeing is perhaps a relationship between the number of COVID cases [in Montreal] and the number of children who are developing Kawasaki, which would then lead you, epidemiologically, to wonder, is it connected?” said Stephen Freedman, a pediatric emergency medicine doctor at Alberta Children’s Hospital in Calgary. "And that’s very possibly the case.”

Dr. Freedman, who is leading an international study of how COVID-19 affects children, surveyed 15 of Canada’s pediatric hospitals early last week and found that only Sainte-Justine had seen anything that might match the mystery syndrome reported in Europe and New York.

“We’re at the early stages of knowing anything, in all honesty," he said.

Toronto’s Hospital for Sick Children has so far not seen an increase in the number of children turning up with Kawasaki-like disease, but a team of specialists at the hospital is working with colleagues at other Canadian centres to make sure such children are identified and properly treated.

“Other geographical areas may be ahead of us in terms of evolution of the pandemic and we suspect SickKids could start to see an increase of these cases as well,” said Jessamine Luck, a spokeswoman for the hospital.

Rosie Scuccimarri, a pediatric rheumatologist and Kawasaki disease expert at Montreal Children’s Hospital, said that parents should seek medical attention if their children have a fever that lasts more than a few days, especially if they are experiencing other symptoms of shock or blood-vessel inflammation.

“I think right now the concern is that people are afraid to come to the emergency room because they’re afraid to catch COVID,” she said.

She reiterated, however, that Kawasaki disease is rare and that the coronavirus – whether linked to the mystery syndrome or not – is generally gentle on the young.

With a report from Kristy Kirkup

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