(Bloomberg) — The coronavirus may have triggered a 30-fold jump in cases of a serious but rare pediatric inflammatory disease, according to an Italian study that provides an ominous warning to other pandemic-affected nations about the risk to children.

A detailed analysis from Bergamo, the epicenter of the Italian Covid-19 outbreak, found 10 cases of a Kawasaki disease-like illness in children, adding to reports of about 90 similar cases from New York and England.

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Kawasaki disease is a rare condition that typically affects children younger than 5. It causes blood vessels to become inflamed and swollen. Typical symptoms include fever and rash, red eyes, dry or cracked lips or mouth, redness on the palms of the hands and soles of the feet, and swollen glands.

While children remain at lower risk than older adults of developing severe complications after being infected with the Covid-19-causing SARS-CoV-2 virus, the research published Thursday in the Lancet medical journal shows that their risk isn’t zero. Cases may occur in the other countries affected by the pandemic, a risk that should be taken into consideration in formulating guidance on when and how children should be allowed to mingle.

“In our experience, only a very small proportion of children infected with SARS-CoV-2 develop symptoms of Kawasaki disease,” said Annalisa Gervasoni, a pediatrician at Bergamo’s Hospital Papa Giovanni XXIII and one of the study’s authors, in an emailed statement. “However, it is important to understand the consequences of the virus in children, particularly as countries around the world grapple with plans to start relaxing social distancing policies.”

Typically, about a quarter of children affected experience cardiac complications, but the condition is rarely fatal if treated appropriately. It’s not known what triggers the condition, but it’s thought to be an abnormal immune overreaction to an infection.

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The Covid-related cases should be classified as “Kawasaki-like disease,” the authors said, as the symptoms in the 10 patients with the inflammatory condition they diagnosed during the pandemic were different and more severe compared with the 19 Kawasaki disease cases they’d observed in the previous five years.

Also, the patients treated during the pandemic didn’t respond as well to the standard therapy — intravenous immunoglobulin — requiring additional steroid medication to counter an aberrant immune response or “cytokine storm” most likely triggered by the coronavirus.

While the incidence of cases during the pandemic appeared about 30 times higher than usual, the Kawasaki-like ailment probably afflicts no more than 1 in 1,000 children exposed to SARS-CoV-2 virus, the authors said.

“We are starting to see case reports of children presenting at hospitals with signs of Kawasaki disease in other areas hit hard by the Covid-19 pandemic,” said Lorenzo D’Antiga, a co-author of the study. “Our study provides the first clear evidence of a link between SARS-CoV-2 infection and this inflammatory condition, and we hope it will help doctors around the world as we try to get to grips with this unknown virus.”