This episode was filmed on May 26th, 2020.

If we have more recent episodes about the COVID-19 pandemic and how it affects children, we will include them in the description and in our COVID-19 playlist. [♪ INTRO]. One of the few comforting things about this pandemic is that kids have mostly been spared.

Children aren't immune to the virus SARS-CoV-2, but they do seem to be only a small minority of those who test positive. Unfortunately, nothing in epidemiology is ever that simple, and we're starting to see evidence of a rare, but serious, complication in children that resembles a condition known as Kawasaki disease. But this condition is very treatable.

So here's what doctors say we should watch out for. On May 14, the US Centers for Disease Control issued an advisory to healthcare practitioners, based on case reports from the United States, the UK, and elsewhere, to be on the lookout for Kawasaki-like symptoms. Kawasaki disease is a rare condition that mostly affects very young children.

It shows up in about ten to twenty out of every hundred thousand children under five. Symptoms include a high, persistent fever and widespread inflammation across the body. This can cause swelling of the walls in certain arteries.

Other symptoms can include swollen lymph nodes, especially near the neck; redness and rashes across the body; and things like diarrhea, vomiting, joint pain, and peeling skin on the hands and feet, especially around finger and toe-tips. Medications can ease the fever and inflammation, but there can be permanent damage if the disease isn't treated. Up to a quarter of untreated children end up with damage to their coronary arteries, which are the vessels that supply blood to the heart.

Now, like we said, Kawasaki disease is usually really rare. So it's definitely strange to see a bunch of cases of something that looks a lot like it pop up at the same time. But that's what a number of doctors and health officials have noticed.

The cases the CDC was warning about seemed to mimic the known symptoms of Kawasaki disease, including persistent fevers and inflammation. It's not clear if these new cases are actually Kawasaki disease, or just something like it. But the symptoms are close enough that doctors first began calling it “Kawasaki-like”.

At least two other names have been proposed, so you might hear people talking about MIS-C in the US, or PIMS-TS in Europe. They're the same thing, it's just that researchers haven't agreed on a name -- or even if it needs a new one. One large hospital in Italy had ten of these Kawasaki-like cases in two months, from mid-February to mid-April, compared to nineteen diagnoses of Kawasaki disease over the past five years.

That study also saw a difference in the average age of cases. Kawasaki disease normally affects kids with an average age of three, but these patients were closer to seven and a half. This could have been down to the small sample size, though.

Doctors in the UK have noticed a similar spike in the number of kids presenting with Kawasaki-like symptoms. And the state of New York has had about one hundred MIS-C cases. New York's governor has said that they and fourteen other states are investigating even more potential cases.

Unusually for Kawasaki disease, some of those cases are in young adults, from their early to mid-twenties. Now, we don't know what exactly causes Kawasaki disease. It's likely a result of something triggering the immune system.

Viruses, bacteria, and environmental causes have all been suggested, though we aren't certain yet. A 2005 study even linked cases of Kawasaki disease to a coronavirus called HCOV-NH, which is similar to one that causes the common cold. Later studies cast doubt on the connection.

But in many of these new cases, the kids had tested positive for SARS-CoV-2 after these symptoms appeared. This may be what doctors are calling a post-infectious inflammatory syndrome. This means it generally shows up later, after the initial viral infection is over.

But we don't know exactly how yet. It could be a case of the immune system overshooting and attacking the body, or it could be something else. The fact that it only shows up after the infection is more or less done might explain why we're only noticing it now, months into the pandemic.

Or, it might just be that in the rush to treat the pandemic and save lives, an uptick in a rare syndrome might simply go unnoticed for a time. This is why the heads-up to doctors from the CDC might be important. Hopefully, doctors -- and parents -- will know to be on the lookout for these rare symptoms, so that kids who are affected can get treated in time.

We here are internet people, not doctors, but we do suggest you call one if your kid shows unusual symptoms. Remember, that's stuff like a high fever, abdominal pain, and feeling extra tired. We'll leave some resources for you parents out there in the description.

But don't freak out, because even with the increased number of cases, this is still super rare. Big picture, it's important to remember that children have an overall low burden of illness from this pandemic. And this Kawasaki-like problem is both uncommon and treatable.

But it's good to look out for things like this. Doctors and families can stay vigilant to avoid permanent effects. Plus, understanding what's going on in these children might help us understand the immune response to the virus, and why the majority of children seem only mildly affected.

It's also a reminder that doctors and scientists are learning more every day about how SARS-CoV-2 affects the body. It's not always what we expect, but it's a problem we can solve. Thanks for watching this episode of SciShow, and thanks to our patrons, who are helping us to bring timely information to everybody during this weird and difficult time.

We really count on y'all, and we are very grateful to have you. If you want to get involved, check out patreon.com/scishow. [♪ OUTRO].