Doctors in northern Italy, one of the world's hardest-hit areas during the pandemic, have reported extraordinarily large numbers of children under age 9 with severe cases of what appears to be Kawasaki disease, more common in parts of Asia.
In Britain, doctors have made similar observations, prompting Health Secretary Matt Hancock to tell a coronavirus news briefing on Monday that he was "very worried" and that medical authorities were looking at the issue closely.
In the United States, a leading paediatric society says it has yet to see something similar.
Kawasaki disease, whose cause is unknown, often afflicts children aged under 5 and is associated with fever, skin rashes, swelling of glands, and in severe cases, inflammation of arteries of the heart. There is some evidence that individuals can inherit a predisposition to the disease, but the pattern is not clear.
England's national medical director, Stephen Powis, told the British briefing he had become aware of reports of severely ill children with Kawasaki-like symptoms in the past few days but stressed it was too early to determine a link with the coronavirus.
"I've asked the national clinical director for children and young people to look into this as a matter of urgency. ... We're not sure at the moment," Powis said.
In Italy, paediatricians are also alarmed.
A hospital in the northern town of Bergamo has seen more than 20 cases of severe vascular inflammation in the past month, six times as many as it would expect to see in a year, said paediatric heart specialist Matteo Ciuffreda.
Ciuffreda, of the Giovanni XXIII hospital, said only a few of the infants with vascular inflammation had tested positive for the new coronavirus, but paediatric cardiologists in Madrid and Lisbon had told him they had seen similar cases.
He has called on his colleagues to document every such case to determine if there is a correlation between Kawasaki disease and COVID-19. He aims to publish the results of the Italian research in a scientific journal.
'MULTI-ORGAN INFLAMMATION'
Ciuffreda said his first case of apparent Kawasaki disease was a 9-year-old boy who came to the hospital on March 21, at the peak of the coronavirus outbreak, with high fever and low blood oxygen levels. He tested negative for the coronavirus.
A scan showed the child had an enlarged coronary artery, a hallmark of severe cases of Kawasaki disease, he said.
"The little boy worried me a lot, with a violent multi-organ inflammation affecting both heart and the lungs," Ciuffreda said. "I feared he wouldn't survive, but surprisingly, in the course of a few days, he took a positive turn and he got better."
Kawasaki disease was anecdotally linked 16 years ago to another known coronavirus, though it was never proven. The research was carried out after another, related coronavirus known as NL63 was found in a baby showing symptoms of Kawasaki disease in 2004.
Ian Jones, professor of virology at the University of Reading in Britain, said the NL63 virus uses the same receptor as the new coronavirus to infect humans, but he also stressed it was too early to draw conclusions.
"We just have to wait and see if this becomes a common observation," he said.
The American Academy of Pediatrics (AAP) has yet to see something similar in the United States, which has the greatest number of coronavirus infections and deaths.
"We are not aware of any reports of this phenomenon in the United States," Dr. Yvonne Maldonado, who chairs the academy's committee on infectious disease, said in an email, referring to a potential link between COVID-19 and Kawasaki-type symptoms.
Dr. Sean O’Leary, a paediatric infectious diseases expert at Children's Hospital Colorado who is part of that AAP committee, said his hospital has seen several cases of Kawasaki this year, but none in the more than 30 children admitted for COVID-19.
"Even if it is related, is a very rare complication," he said. "If it were more common, we'd already have a pretty good idea about it in the United States."