(CNN) The US Centers for Disease Control and Prevention issued a health advisory to thousands of doctors across the country Thursday, advising them to be on the lookout for a troubling new syndrome that may be associated with Covid-19 infection.
The syndrome, called multisystem inflammatory syndrome in children (MIS-C), has been seen in children across Europe and in at least 18 states, plus Washington, DC.
Doctors in the UK first alerted other doctors to the syndrome in April. Since then physicians in other countries, including Italy and France, have reported clusters of similar cases.
"Beginning about four or five weeks ago, in Europe they stared to describe a form of what really sounded like toxic shock," said Dr. Jeffrey Burns of Children's Hospital and Harvard Medical School in Boston. Burns has been coordinating a series of regular video chats among doctors around the world comparing notes on pediatric cases of Covid-19.
"There were just a few at first and then more," Burns told CNN.
At first, the cases were believed to be Kawasaki disease, a rare, inflammatory condition that usually involves the major arteries and the heart. But there were too many cases for it to be Kawasaki, and the doctors agreed it was a different inflammatory syndrome. Many, but not all, of the children tested positive either for current Covid-19 infection, or a past infection.
It's only rarely fatal and most children recover, Burns said.
"During March and April, cases of COVID-19 rapidly increased in New York City and New York State. In early May 2020, the New York City Department of Health and Mental Hygiene received reports of children with multisystem inflammatory syndrome," the CDC health advisory reads.
New York Governor Andrew Cuomo said earlier Thursday that the state Department of Health was investigating 110 cases of the syndrome. "It tends to present in children who were exposed to the Covid virus and actually now have the antibodies ... or still test positive for the Covid virus," Cuomo said at a news conference in Albany.
The CDC said it was still gathering information about the cases.
"There is limited information currently available about risk factors, pathogenesis, clinical course, and treatment for MIS-C. CDC is requesting healthcare providers report suspected cases to public health authorities to better characterize this newly recognized condition in the pediatric population."
The advisory provides a case definition to guide doctors: