A 15-year-old describes getting a rare post-COVID illness, starting with a rash and turning into loss of heart and kidney function

• Children who get COVID-19, whether mild or severe, are at risk of developing MIS-C, a life-threatening syndrome.
• 15-year-old Abie Martinez, who had a mild COVID-19 case in 2020, shared his story about losing heart and kidney function with Insider.
• "It was a scary experience," his mom said.

When 15-year-old Abie Martinez got COVID-19 last December, it was not a big deal.

"It was just a little cough, and then my loss of taste and smell," he said, adding "I got it back pretty quickly."

After his infection subsided, he continued his usual routines: heading to the gym about three times a week, and going to school in person. It wasn't until over a month later, on January 25, 2021, when he started to feel a strange, sharp kind of pain in his left leg and in his neck.

"My shoulders would ache every time I would do something," he said, and "it would hurt to stand up all the way."

Abie didn't know it at the time, but he'd developed multisystem inflammatory syndrome in children, MIS-C. It's an exceedingly rare condition that appears to predominantly affect children after contracting or being exposed to COVID-19. While it is not common - the US has counted 4,100 cases of MIS-C in kids since the pandemic began - doctors are urging children and parents to be aware that it is not something to brush off.

The day after Abie's muscle aches began, he became sensitive to light and noise. By Wednesday, a large red rash appeared on his inner arm.

His symptoms became severe over the course of the week, including fever, diarrhea, and extreme fatigue.

"I had really bad back pains and then I kept throwing up," he said. "My body just wasn't working."

'The most seriously ill children that we see with COVID-19'

Kids who get MIS-C after infection are "the most seriously ill children that we see with COVID-19," according to Dr. Andrew Pavia, chief of pediatric infectious diseases at the University of Utah who has seen 100 cases of MIS-C in children during the pandemic.

Pavia says "it's hard to predict who's going to get" MIS-C, because the syndrome seems to affect kids like Martinez, who've had a very mild case of COVID-19, just as often as it does children who've had a more serious illness.

If left untreated, MIS-C can lead to organ failure and death. So far, at least 37 children have died from MIS-C in the US, since the CDC began tracking cases in May of 2020.

It's still not clear to experts what causes the condition. More than half of the confirmed MIS-C cases nationwide have been in males (60%), and a majority of the kids are Black, Hispanic, or Latino, according to the CDC.

Martinez was hospitalized for five days with major heart issues

On Friday, five days after his initial symptoms started, Martinez was medivac'd to a hospital in Salt Lake City, where he stayed for five days of treatment, as doctors worked to stabilize his heart rate and blood pressure.

His cardiologist, Dr. Dongngan Truong, administered epinephrine and norepinephrine to regulate his blood pressure, as well as immunotherapies including steroids and pooled antibodies (IVIG).

Six months later, Martinez feels almost back to normal now, with just "little chest pains" sometimes, he says. He's been swimming this summer, and he thinks he might be able to participate in gym class at school this fall, something he wasn't able to do safely after his MIS-C treatment.

He goes in to the hospital for check ups every three months to make sure his heart's recovering.

"It was a scary experience," Martinez's mom, Cendy Marquez, said - describing watching his kidneys shut down and seeing the damage to his heart.

"His kidneys look great, and his heart's doing really, really good," she said, though she is still encouraging him to not "overdo it" as his body recovers.

"I kind of have to remind him, just because he's so young and active," she said. "Just relax."

Experts urge parents to send their young unvaccinated kids to school in masks

Dr. Pavia is concerned that more cases like Martinez's could surface in the weeks ahead, given the recent surge in pediatric COVID-19 cases and hospitalizations nationwide. According to a new report from the American Academy of Pediatrics, kids now make up 19% of reported COVID-19 cases nationwide, a dramatic jump from the 14.3% cumulative average earlier in the pandemic.

"We just encourage parents not to blow things off as gastroenteritis or a summer cold," Pavia said. "We really want all parents to be aware of the possibility."

With initial symptoms including a high fever, stomach pains, vomiting and diarrhea, MIS-C is not a subtle condition.

The best way to protect children as they head back to in-person learning, with the Delta variant spreading, is to get as many teachers and students who are eligible vaccinated, and then to mask everyone up in the classroom, to prevent the spread of the disease to young kids who haven't gotten inoculations.

"This notion that, 'Oh, it's OK for kids to get COVID' is really a bad notion," Dr. Tina Tan, a professor of pediatrics at Northwestern University, said during a recent Infectious Diseases Society of America briefing.

"Send your child to school with a mask," she said.