The illness, which the Centers for Disease Control and Prevention (CDC) called multisystem inflammatory syndrome in children (MIS-C), was first reported in Britain in late April.
"Healthcare providers who have cared or are caring for patients younger than 21 years of age meeting MIS-C criteria should report suspected cases to their local, state, or territorial health department," said the CDC.
The condition had previously been referred to as Pediatric Multisystem Inflammatory Syndrome (PMIS) by the state of New York, where there have been more than a hundred reported cases, including at least three deaths.
Doctors who have treated the illness say patients sometimes have symptoms similar to a rare condition called Kawasaki disease, which causes blood vessels throughout the body to swell, leading to extreme pain.
Sunil Sood, a paediatrician at Cohen Children's Medical Center in New York, told AFP that some children had very mild forms of illness, but about half of the patients that he and colleagues had seen had to be treated in intensive care for heart inflammation.
