By Julie Steenhuysen

CHICAGO (Reuters) – U.S. scientists are working to understand a rare, life-threatening inflammatory syndrome in children associated with exposure to the new coronavirus by quickly assembling clinical trials and patient registries.

Cases were first reported in Britain, Italy and Spain, but now doctors in the United States are seeing clusters of kids with the disorder, which can attack multiple organs, impair heart function and weaken heart arteries.

This emerging syndrome, which may occur days to weeks after a COVID-19 illness, reflects the surprising ways that this entirely new coronavirus infects and sickens its human hosts.

At least one child in Britain has died. No children are believed to have died so far in the United States, “but that could change,” said Dr. Sean O’Leary, a pediatric infectious disease expert at Children’s Hospital Colorado who serves on the American Academy of Pediatrics committee on infectious disease.

O’Leary said efforts are getting underway to collect information on the disorder, dubbed a “Pediatric Multi-System Inflammatory Syndrome Potentially Associated with COVID-19.”

“Every academic center I know of is looking for these cases and trying to systematically track them,” he said.

The New York Department of Health on Wednesday reported 64 cases of the new syndrome as of May 5, and is calling on hospitals to immediately report any cases to the department.

It did not say how many children tested positive for the coronavirus, but said it believes the syndrome is potentially associated with COVID-19.

State public health officials are asking hospitals to perform a nasal swab PCR test looking for active infections, as well as antibody tests that could detect prior exposure to the virus, known as SARS-CoV-2.

Dr. Steven Kernie, a pediatric critical care expert at NewYork-Presbyterian/Columbia University’s children’s hospital, said 15 to 20 children have been treated for the condition in the intensive care unit.

“It’s still a rare condition. But it’s rising,” Kernie said.

The U.S. Centers for Disease Control and Prevention said it is working with the Council of State and Territorial Epidemiologists and other groups to gather data to better understand and characterize the syndrome, according to an emailed statement.

The aim is to develop a case definition that would allow the CDC to track the cases and advise doctors on how to care for these patients.

Not every child that has developed the condition has tested positive for the novel coronavirus, but enough have for doctors to believe the conditions are linked.

For most children, COVID-19 disease is mild, and children are far less likely to be hospitalized with COVID-19 than adults, according to the CDC.

“Children seem to laugh off COVID-19 most of the time,” said Dr. Jane Newburger, a pediatric cardiologist at Harvard’s Boston Children’s Hospital. “But rarely, a child will develop this hyper-inflammatory state.”

Newburger said there appears to be a spectrum of illnesses, with some children coming in “very sick, even in shock.” Most have a fever and impaired function in one or more organs.

Some children get sick very fast and need to be in a pediatric intensive care unit, while others can be cared for in a regular hospital ward, she said.

The syndrome was originally thought to be linked with Kawasaki disease, which in severe cases causes inflammation of the heart arteries.

“The children we’re seeing are sicker than the typical child with Kawasaki,” Kernie said. “What we worry about is primarily the development of coronary artery aneurysm, which can be life-threatening.”

A conference call with experts over the weekend organized by Boston Children’s drew some 2,000 participants.

Researchers are focused on testing to confirm a link with COVID-19 and the collection of blood or DNA to study whether some children are genetically predisposed to develop the condition.

Heart specialists are worried about the long-term effects of the syndrome, especially if heart arteries become weakened.

“It’s a very scary illness,” said Dr. Eric Topol, a cardiologist and director of the Scripps Research Translational Institute in La Jolla, California.

Topol pointed to eight cases described in The Lancet on Wednesday in which one child developed an aneurysm and another died from stroke.

Since submitting that paper a week ago, the team from Evelina London Children’s Hospital reported managing 20 more children with the condition.

(Reporting by Julie Steenhuysen; Editing by Bill Berkrot and Grant McCool)