(NEXSTAR) – A new study in JAMA shines light on COVID-19 in kids and the frightening illness Multisystem Inflammatory Syndrome in Children, or MIS-C.

According to a case study that included 539 patients with MIS-C and 577 patients with severe COVID-19, patients with MIS-C were more likely to be Black and ages 6 to 12 years old.

The patients with severe COVID-19 were often either younger than 6 or older than 12.

The researchers also found that children with MIS-C were more likely to have been previously healthy than those who contracted COVID-19.

The symptoms for MIS-C patients tended to be far more severe, as well. They were more likely to require treatment in an intensive care unit, and their symptoms more often included heart problem and inflammation.

About the same number of patients in the study needed respiratory support and the same small number of patients died: 10 with MIS-C and 8 with severe COVID.

About 2,000 cases of MIS-C have been reported in American children since May 2020, according to the Centers for Disease Control and Prevention, though the case load is likely much higher. Thirty deaths have been attributed to the syndrome.

The illness appears to crop up weeks after a COVID infection or exposure — even if the case was asymptomatic or mild. The disease has also been reported, with less frequency, in adults.

“MIS-C is basically a post-infectious inflammatory syndrome,” meaning the disease causes inflammation in various parts of the body, said Dr. Roshni Matthew, a clinical associate professor in pediatric infectious disease at Stanford University. 

Symptoms include fever, rash, pink eye, gastrointestinal issues, swelling of the lymph nodes and swelling of the hands, feet and face. 

In severe incidents, MIS-C can affect the heart — these are the cases that have typically resulted in death, said Matthew.