MILWAUKEE — Over the course of the pandemic, Wisconsin’s kids are the ones who have seen the most cases.

According to Department of Health Services data, residents under 18 have gotten infected more often than any other age group in the state. And though children are generally at a lower risk for severe COVID-19 outcomes, they are uniquely vulnerable to one problem: Multisystem inflammatory syndrome in children, or MIS-C

Wisconsin reported its first death from MIS-C last month. So what exactly is the rare illness that affects some kids after they come across the novel coronavirus?

As it turns out, that question doesn’t have a simple answer. Here, we break down some of what scientists know — and are still learning — about MIS-C and its effects in the Badger State.


The basics

​MIS-C doesn’t seem to be caused by an active infection, but by how the body reacts to a COVID-19 exposure.

“MIS-C is seen as a post-infectious inflammatory syndrome,” explained Dr. Frank Zhu, medical director of infection control and prevention at Children’s Wisconsin. “So what that means is after an infection — and in this case, it would be with COVID-19 — your body eventually, for whatever reason, gets an immune system response that's much greater than it should.”

The condition occurs most often in kids aged 5 to 11, Zhu said, and usually shows up about a month after an initial COVID-19 infection. (There’s also a version of the condition for adults, known as MIS-A, but this is even rarer,  Zhu added.)

There are a few key ingredients for an MIS-C diagnosis, including a sustained fever, inflammation and evidence of a prior COVID-19 infection or exposure. Beyond that, a wide range of symptoms can also show up: Rashes on the skin, bloodshot eyes, vomiting, diarrhea, dizziness.

Most of the patients at Children’s Wisconsin have come in with “not terribly severe symptoms,” Zhu said, but with that fever and inflammation present.

In some cases, though, MIS-C can be more intense. A severe case might involve a decline in heart function, inflamed lungs and pneumonia-like symptoms — almost looking like a severe case of COVID-19, Zhu said.

To treat kids with MIS-C, providers have to bring down that inflammation, Zhu said, usually through some combination of an antibody infusion, steroids and other medications. The treatment and the symptoms have a lot in common with Kawasaki disease, another inflammatory condition that mostly affects kids.


Wisconsin's numbers

​As of the latest DHS data, 187 cases of MIS-C have been reported in Wisconsin. The average age for MIS-C patients was 8 years old, the DHS reports. 

That means the condition is still very rare: With hundreds of thousands of total COVID-19 cases reported in Wisconsin kids, MIS-C has only shown up in a fraction of a percent of infections. The Badger State is pretty much in the middle of the pack in the U.S. when it comes to MIS-C rates, Zhu said.

“We're not an outlier in terms of numbers of cases,” Zhu said.

Over the course of the pandemic, Children’s Wisconsin has seen MIS-C spikes follow about a month behind general COVID-19 surges, Zhu said. 

According to monthly totals from the DHS, the highest MIS-C case counts happened in December 2020 and January 2021 — in the midst of Wisconsin’s first winter surge — and in January 2022 as variants were sending cases soaring. 

Across the country, though, CDC data show that MIS-C cases have not yet spiked as much as expected in the wake of the omicron surge, Zhu said — even though the latest variant brought higher case counts in kids. January 2021 still marks the highest nationwide peaks for MIS-C.

It’s still early to say, but MIS-C “may be something that we see more in the past than moving forward,” Zhu said. 

Like many pandemic outcomes, MIS-C has also hit certain communities harder than others: The DHS reports that more than half of cases occur in racial and ethnic minority groups, which only make up 20% of the state. Black and Hispanic children have especially seen disproportionate MIS-C impacts in Wisconsin, the state reports.


More to learn

​Something else MIS-C has in common with other pandemic outcomes: There’s still a lot for scientists to uncover about it.

That includes the question of what exactly causes the condition in kids. Most children with MIS-C test positive for coronavirus antibodies — meaning they’ve had a brush with the virus in the past, even if they’re not sick with COVID-19 at the moment.

For kids who do experience MIS-C, the immune system seems to be reacting much more strongly than it needs to, Zhu said. But as the CDC guidance explains, it’s still unclear why only some children will experience this inflammatory condition, and whether any other health conditions could lead to a higher MIS-C risk.

Zhu said one of the biggest challenges for the future will be figuring out how to actually diagnose MIS-C cases. Right now, he said the definitions include a very broad list of symptoms, and there’s no single test that can decide whether someone has MIS-C.

“You want to catch all the cases you can so they can be reported and analyzed and studied,” Zhu said. “But as more and more children are exposed to COVID, I think we'll start to have to question whether or not this case definition is the best way to officially diagnose MIS-C.”

It’s also going to take more time — and more data — to tease out whether factors like the rise of the omicron variant and the availability of COVID-19 vaccines for kids could make MIS-C rarer, Zhu said. 

The good news is that, according to Children’s Wisconsin, most of their MIS-C patients have gotten better with treatment and have not faced long-term health issues from the condition. The hospital is working with other groups across the country to keep studying the condition and its long-term effects on kids.

Getting more answers about MIS-C will probably require some patience, though. Even Kawasaki disease, which has been around for decades before MIS-C showed up, still doesn’t have a known cause.

“The greatest questions that remain are ones that are going to be here with us for a long time,” Zhu said.