It began in Europe about two months ago, has spread to cities along the U.S. east coast and is now being reported in Montreal: clusters of a rare and mysterious illness in children that may be linked to COVID-19.

The latest alert comes from New York City’s health department, which, on Monday, reported 15 cases of children ages two to 15 arriving in city hospitals with “multi-system inflammatory syndrome.”

The symptoms vary depending on the affected organ system, but include a persistent fever, rash, abdominal pain, vomiting or diarrhea. Five children required mechanical ventilation, though no deaths have been reported.

When noses were swabbed to check for active COVID-19 infections, four children tested positive, and 10 negative. One was initially “indeterminate” and then negative. However, when their blood was sampled, six of the “negatives” had antibodies to the virus, suggesting they had been exposed some time in the past.

The NYC bulletin, which follows a similar alert issued by British health officials, comes as Quebec prepares to reopen elementary schools and daycares starting May 11 outside Montreal, with the city scheduled to follow one week later. Ontario has said schools will remain shuttered until at least the end of May. In B.C., “education as we know it” likely won’t return until September, Premier John Horgan has said, while in Alberta, schools “as a general rule” will remain closed for the balance of the academic year, stated Premier Jason Kenney.

On Monday, New Jersey Gov. Phil Murphy announced schools would remain closed until at least the fall “to protect the health of our children.”

Quebec, meanwhile, says its gradual and non-mandatory return to school schedule has been endorsed by Quebec public health. Elementary classes will be limited to 15 students max. per class, children will be seated two metres apart and teachers may or may not wear masks.

“We will not comment on decisions made by other jurisdictions,” Francis Bouchard, press attaché to Quebec Education Minister Jean-Francois Roberge said in an email.

We will not comment on decisions made by other jurisdictions

“We will remain very attentive to the situation and if public health recommends us to postpone the opening of schools, we will not hesitate for a single instant to do so,” Bouchard said. “You have to trust Dr. Arruda (Horacio Arruda, Quebec’s director of public health) and his team. They are the experts.”

As Quebec teachers prepare their classrooms, doctors at Montreal’s Sainte-Justine Hospital are poring over the 15-20 cases of children that developed what seems to be the same hyper-inflammatory illnesses reported in New York children, as well as children in Italy, the U.K., France and Spain. The cases have overlapping symptoms with toxic shock syndromes and Kawasaki-like disease. Kawasaki causes inflammation and swelling in blood vessels throughout the body, including the coronary arteries. While the vast majority of kids with Kawasaki disease do well when diagnosed and treated early, if diagnosed late they can be at risk for coronary artery aneurysms, a dilation of the blood vessels that provide oxygen to the heart.

In the Montreal cluster, “in every case we failed to detect” the virus that causes COVID-19, said Dr. Elie Haddad, head of paediatric immunology at Sainte-Justine. They closed the files, thinking, “Ok, that’s inflammation.” It looked and behaved like a Kawasaki-like disorder, Haddad said. Then came reports out of Europe, where children with the same mystery illness showed antibodies against SARS-CoV-2.

It’s entirely logical to think the pandemic virus could cause a delayed, post-viral infection in some children, Haddad said. Kawasaki is thought an inflammatory response: the body mounts a response to a virus, but the response is exaggerated and targets some of the body’s own blood vessels.

If that’s true for the COVID-19 virus, “we want to understand why? How does it work,”  Haddad said. So far, there’s no definitive link. It’s possible the children were infected with COVID-19, recovered and developed the inflammatory syndrome from some other pathogen entirely.

“We are learning every day with this virus,” Haddad said.

All of the children were easily treated and recovered, though one child required admission to intensive care.

The symptoms, including redness inside the mouth, conjunctivitis (pink eye), pain in the hands and feet, fatigue and fussiness — “they are not happy in the arms of their mothers,” Haddad said — stand out, because with COVID-19, children rarely get severe complications. In Canada, children under 19 account for about five per cent of confirmed cases overall.

It’s not known why children tend to have mild disease, or how transmissible the virus they’re harbouring. One study in Germany found the viral load, the amount of virus children carry is probably similar to adults. “I think we would be reassured if their amount of virus was a lot lower, so that if they were to sneeze, cough, drool, put their hands on things, they’d be less likely to transmit,” said Dr. Stephen Freedman, a pediatric emergency medicine doctor at Alberta Children’s Hospital in Calgary.

Classic viral infections like influenza tend to be more severe in young infants and children. The case is different with COVID-19. Fewer children have developed severe pneumonia, and deaths have been extremely rare.

There’s no clear answer as to why. It may be that their immune systems aren’t as hyper-responsive, said Freedman, who is leading a global study into how COVID-19 affects children.

Several U.S. hospitals have reached out to Freedman to say they’re seeing large numbers of Kawasaki disease cases potentially tied to COVID-19. When he surveyed 15 children’s hospitals in Canada last week, Sainte-Justine appeared to be the only one with a cluster. More common were COVID toes, the swollen, red, purplish digits on some children’s feet that, fortunately, “appears to be a benign entity,” Freedman said.

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